Too many hill towns? Do they all look alike?

Those hill towns are all different.
On our last Tuscan trip, we visited Siena, Certaldo, San Gimignano, Volterra and Orvieto by rental car. I would have loved to have seen Civita as it's just a short distance SW of Orvieto.
Siena is best visited by a bus that parks across the street from the Florence train station--to the right of McDonalds. Traffic there is congested and parking is difficult to find.
I would bypass on Pisa and Lucca as they're west of Florence and a different direction from the rest of the hilltowns.
You could visit Orvieto by train from Florence, but it's really best to see Tuscany and Umbria by rental car. Many tourists drive as far as Orvieto and take the 70 minute train from there into Rome Termini. The Hertz rental office is across the street from the Orvieto train station.

I agree with David that all the towns you name are different. Pisa isn't exactly a "hill town". It can be combined with Lucca as a long daytrip (spend most of your time in Lucca). Orvieto and Civita di Bagnoregio can be another day trip (spend most of the day in Orvieto and get an early start). If I had to delete anything, it would be Civita. Siena should have a day of its own, it is very different early or late in the day than when all the other daytrippers are there.

Are you leaving any time for Firenze?

You can check train prices on Trenitalia (get the English version by clicking the flag icon), if your trains are not long distance, just plug in a day (same day of the week as you expect to travel) within seven days of the day you search to get an idea of regionale train prices. These tickets don't need to be booked in advance, anyway.

Rome2rio.com can give you time/cost estimates for different modes of transportation (costs are not that reliable).

I've been to all but Pisa and agree that they are all different, BUT that seems like a lot to cover in 4 days including driving to and from plus giving yourselves time to see them. If I were going to drop one, I would drop Civita di Bagnoregio as it was my least favorite. It is not really a town that is still lived in and seemed filled with deserted buildings and stray cats. I know Rick and many others like it but it just didn't do anything for me. I also have an issue with heights and had no idea from the pictures how high the walkway is over to it.

I loved Orvieto, Volterra, Lucca and Siena.

I went to a very little visited hill town from Lucca. Braga is about 1.5 hours more or less from Luccca, through beautiful mountains and streams.
From the train station there are buses that go to the hill town of Braga.
Surprisingly, there is a strong Scottish influence, due to a pattern of migration from Braga to Scotland.
Since I always look for lesser visited places, this was perfect, not too mention beautiful, unusual, and tranquil.

Personally, if you rent a car, you should use it to visit places where a car is more efficient than public transportation. Therefore a car should be used to visit any of the following:
Chianti Hills, San Gimignano, Certaldo, Volterra, Monteriggioni, Pienza, Montepulciano, Montalcino, Val D'Orcia (San Quirico, Buonconvento) and many other places in the area. For example, Volterra can be easily done together with San Gimignano (both IMO are must see towns) and maybe even Monteriggioni (another must see fortified village).

Siena is a must do town and in the general area where the above towns are located, but the car is of no use there, so maybe you could visit it from Florence without a car and save yourself a car rental day (it's 70 min away by bus from Florence). Siena can easily take several hours to visit. If you do it by car, take advantage of the car and drive through the Chianti Road (SR 222).

Orvieto and Civita are kind of far from Florence and the rest of the places you want to visit in Tuscany and would be best done from Rome (are you in Rome at all during your trip?) or maybe on route between Rome and Florence. Unless you are going to Rome in this trip, I would ditch both because it's a detour from the rest.

Lucca and Pisa are next to each other and can be done on the same day. Neither one is a hill town (both are flat)
Lucca is a pretty fortiified town and I think it deserves most of the day if you visit Lucca and Pisa together.

Pisa is a one trick town with only one square to see (the Field of Miracles) which contains leaning tower, cathedral, baptistery, cemetery. Two hours are enough. In fact, since you are going to the Cinque Terre later from Florence, and you will need to change trains in Pisa, I would visit Pisa in between train changes. Just deposit your luggage at the station luggage storage, visit Pisa, then retrieve your luggage and proceed to the Cinque Terre.

Another alternative is not to return the car in Florence, rather go from the Tuscan towns, directly to Lucca/Pisa by car, then from there proceed by car to La Spezia (next to Cinque Terre) where you can return the car. Then from La Spezia take the train to the Cinque Terre (10-15 min). This is actually what I would do in your shoes.

So this is my proposed itinerary:

day 1: rent a car in Florence, drive the Chianti Hills all the way to Siena, visit Siena.
day 2: Val D'Orcia area (Pienza, Montepulciano, Montalcino, Buonconvento)
day 3: Monteriggioni, San Gimignano, Volterra
day 4: Pisa/Lucca, return car at La Spezia (Cinque Terre)

Or spread more if you have any extra day.

We spent a night in Lucca on our way from Florence to the C.T. After departing from Lucca we stopped in Pisa for an our or so, before arriving in Vernazza. They have a place at the Pisa train station to store your luggage. Why not avoid driving the car back to Florence and drop it in Lucca instead?

Wow, what a great forum and great participants! Many thanks to all for informative comments - especially to Roberto from Fremont.

Michael

They are all different. My favorites are Maltocino and Montepulciano. Volterra is also really nice. Not sure Sienna is worth the stop, the others are smaller and more fun. Car is the only way to do Tuscany. The Duomo in Pisa is magnificent, rivals St. Peter's. Have fun. Going back in April!

I don't think there are rental agencies in Lucca anymore, so you can't drop the car there. La Spezia is by far the best option since you are going to the Cinque Terre.
Sine the La Spezia rental offices close on Sat afternoon and Sunday all day, if you happen to return the car on a weekend then the second choice is to return the car at the Pisa Airport (always open). Then from Pisa airport go to the train station (shuttle bus or taxi) and take the train to the Cinque Terre (one train change in La Spezia).

FWIW, Lucca is not a hill town. It's on a flat plain. It's charming enough, but don't expect the beautiful vistas that you get from places such as Orvieto, Siena and CDB.

Michael,
I have been to numerous Tuscan hill towns on several different trips. I have gone back and visited some a second time because I had a such a great time on the first time around. I do agree with what most of the posters have said. I do want to add that it is possible and easy to drive to Siena. We did it last year on the day of the Palio and parked at the train station parking lot and took the escalator and walked to the city center. (This is about 1 mile). One point that should be made is that even if the distances seem small, it takes longer than expected to drive everywhere. This is not necessarily a bad thing because the vistas are stunning. However your trip will be more enjoyable if you have reasonable expectations. If you prefer to linger at breakfast drinking an espresso or cappuccino, like I do, your time for day trips is shorter. However, for my wife and I, that is an enjoyable part of vacation. You need to know how the four of you prefer to travel and then plan accordingly. We spent an entire day in Montepulciano and never made it to Pienza. But that was OK for us, but may not be for you. You do want to do a little reading and then decide if there are towns that YOU have to visit. If you are a wine enthusiast, Greve, Montecino, or Montepulciano may be high on your lists. If you would like to see craftsmen at work, Volterra may be the place to visit the alabaster shops. I agree that Orvieto is perfectly situated for a stop between Firenze and Rome (preferably during truffle season). We visited Pisa on the way to the CT and stored our bags at the train station. I am not sure if that service is still available, but the couple of hour stop in Pisa was perfect. My favorites have been Volterra, Montepulciano, Siena, and Greve or other Chianti town near a winery. I am not sure how helpful any of this is, but have a great time!

remove Pisa and Lucca, add Cortona and Assisi. Want spectacular views? These two have them.

Michael,

"and take the train to CT (if I can get an answer to my previous post.)"

You have lots of answers now in your post about travel by train to the Cinque Terre.

The people in my family get different things out of travel, so I look for different kinds of experiences that they can dig into. Over nighting in a town where there is a great morning market adds variety. The food tours which are popular in some cities in Italy please the foodies in our family. I look for great short hikes that get us out into the countryside, or city walks by night. On our next trip we're staying in an agritourismo with a substantial organic garden (my husband and I are avid gardeners). I think experiences like this build another layer of sense-of-place to a trip.

Lia, I love your approach of trying to plan for a wide variety of experiences that you and your family are particularly interested in. That's one of the reasons we always try to find lodging right smack in the place we want to see. Being able to walk out the door first thing in the morning and already be at your destination is hard to beat.

I agree with Jim on Cortona and Assisi.
And my wife absolutely loves Anghiari and Arezzo, so I'll throw those in the mix too if you are considering Eastern Tuscany.

I'm not sure if I understand your itinerary. Are you basing yourself in Florence and making day trips to Orvieto, Siena, etc. Or, are you doing Florence first, getting a car, basing elsewhere and then returning to Florence?

Driving from Florence to Orvieto is two hours which would make for a very long day. I agree, Cortona and Assissi are absolutely amazing and not just full of tourist shops.