Should we stay in Volterra or just daytrip there?

I stayed 2 nights in Volterra a couple of years ago and really enjoyed it. Personally, I'd recommend that over a day trip from Florence. Taking a bus from Florence does require a change in Colle di Val d'Elsa, but the 2 buses are timed to coordinate. There are other ways to get to Volterra, depending on where you're traveling from. For example, I took a train to Pontedera (on Florence-Pisa line) and a direct bus from there to Volterra. A hotel reservation would be wise, especially on a weekend.

Volterra is very small, there is an interesting museum, and the Roman ruins to see. If getting there isn't longer than 2 hours in transit, you can see the town in one day. It shouldn't be overwhelmed with Twilight fans if they want to see the actual clock tower, and square from the movie (but the movie added a fountain that doesn't really exist) since the movie was actually filmed in Montalcino not Volterra. We didnt' see any vampires there, but did see a bunch of Etruscans....

Actually Twilight was filmed in Montepulciano, not Montalcino. But the point remains true - it wasn't filmed in Volterra. Have a great time.

"Do vampires really come from Volterra?" Yes. although some think maybe they come from St. Helens High School (the OP lives in St Helens, is this a coincidence? how about it, Ray? much of 1st film was filmed near where the OP lives, including St Helens High School, per IMDB)

Volterra is lovely and we were just here in September. Visited as a daytrip from from San Gimignano where we were staying in an agriturismo just outside town. Had been to Volterra previously a few years ago and again as a daytrip. You can see the town easily in a day but it would make a nice place to stay too. In Sept. the town was not overwhelmed by Twilight fans but then most kids would have been back in school. As a previous poster stated the movie was filmed in Montepulciano but a few minute were filmed in Volterra and the TI was running that clip over and over. Very proud of that!

'Twilight' fans have also been flocking to Saint Helens. A total of 4 of them last month alone! They made the mistake of sampling the high school's cafeteria food...and lets just say they're not immortal.
Maybe I should avoid any cities that have a connection with the movie.

Most Italian vampires come from Milano- home to the biggest banks

I think it's perfectly fine as a day trip. Volterra is lovely. About a year ago, there was a lot of Twilight stuff in the shops, even ads in the TI office, all of which was disappointing but easy enough to ignore. Actual fans in the city, not so much. If you have to transfer in Colle di val d'elsa, it would be worth checking out that town as well. I think we only spent about an hour there, but it has a nice little old center (the high part of the town accessible by elevator) with a lot of really beautiful crystal shops.

Personally I would just daytrip to Volterra but if you are wanting a relaxing respite from hectic sightseeing elsewhere then you might want to stay overnight. Personally, I don't think I'd enjoy staying there overnight & certainly not 2 nights. It was a beautiful town & I'm really glad I visited, but it would be a little too quiet for me for 2 nights. Be certain to visit the Etruscan Museum in Volterra; there are a lot of interesting artifacts there. We did a half-day tour with a tour guide by the name of Annie Adair (an expat living in the area). I saw her in Rick's show about Volterra and her rates were reasonable and she really brought the town alive for us & we learned things that we otherwise wouldn't have known. We day-tripped from Siena to Volterra & after our half-day tour with Annie, we walked around for a few more hours, had lunch & then left. For us, it was the perfect amount of time in Volterra. Have a great trip.

At this point in our trip I think we'll be looking for a few relaxed days. Col di Val D'Elsa looks really nice in photos. Maybe a couple of hours there would be good as well.

On our last Italy trip in Sept. 2010 my husband and I stopped in Colle di Val D'Elsa for a quick look. We were on our way from San Gimignano to Monteriggione. It is worth a quick look but not lots to see. They make lots of crystal glass in the area and we stopped in a workshop or 2. The approach to Colle from Monterig. is beautiful as it sits high on top of a hill.

I have day tripped from Florence my last 2 trips to Italy, but this coming year, I will use some other town as a base. It is just too difficult to keep a car, park it, avoid the ZTL, etc. in Florence. We may base somewhere near Florence, such as Fiesole, or find a hub out in the countryside where it will be quieter and less traffic.