Siena as a base

Jim, Siena is not the best for train travel. The train station is about 2 km outside the center. The bus from and to Siena is usually the better option. See:
http://www.sitabus.it/sita-toscana/Firenze-Siena2010.pdf http://www.sena.it/index_e.htm http://www.trainspa.it/train04/extraurbano.pdf

The train station in Siena is about a 15 minute walk downhill from the city center. It takes longer to walk up. :-) There are busses, though, from the station to Piazza Matteotti and other stops close to the center. Once up the hill, it's an easy town to walk around. We stayed three nights and took one guided tour, then drove one day to Volterra, but other travellers we met assured us we could have done Volterra on a bus (they also did San Gimignano via bus). As mentioned, check the schedules and see what you can live with on the bus. You give up some flexibility, but gain peace of mind that you don't have to drive! I can highly recommend a B&B for you: Antica Residenza Cicogna. Check them on Trip Advisor. Super nice people, great breakfast spread! Also, Tours By Roberto does some great tours out of Siena.

Jim Siena is a great base for going to the places suggested. Not sure what your concerns are about "avoiding" a car. If it is a $$ issue, then the advices about buses and train are well stated, but I believe public transport is limiting and can be time consuming. If it is concern about difficulty of driving in Italy, then you have no concerns from living in Dumfries. Driving in the countryside outside Siena is like driving in Dumfries in the 1950s. Driving on the one main road 4 lane highway between Siena and Assisi is like driving in Dumfries in the 1970s. Nothing about the places you want to travel to is as difficult or nervewracking as driving in Metro DC in the last 30 years!
Whether by public transport or by car, you will enjoy being based in Siena.

Jim, Skip is right. Driving in Tuscany is not difficult & it would make getting around a lot easier. You wouldn't be tied to a bus schedule and could come and go as you please & wouldn't have to catch a bus or taxi to/from the train station in Siena, etc. We used Siena as a base in Tuscany (stayed in an agriturismo) & rented a car to get around. We drove to Volterra, Pienza, Montepulciano, San Gimignano & Lucca. We brought our GPS from home & had no problems getting around. In fact, my husband quite enjoyed driving there. Part of the fun was simply driving around & being able to stop whenver we saw a photo-worthy vista, etc. You can rent & return the car right in Siena for convenience.

My wife and I would like to thank everyone for their help. We now have a good idea as to our choices and look forward to putting your suggestions to good use. This was our first time using Rick Steves' helpline and we are very impressed with how smoothly it all works. Best of all, we have so many experiences from which to draw. Thanks all . . . Jim

And if you "honest to goodness" really prefer NOT to drive, rest assured that you can reach each of the following towns from Siena by round-trip public bus: 1. Florence 2. San Gimignano (connect at Poggibonsi) 3. Volterra (connect at Colle Val d'Elsa) 4. Montalcino 5. Pienza 6. Montepulciano 7. Pisa Airport (with short city bus connection to Pisa) 8. Arezzo
9. Orvieto (Trenitalia train w/connection at Chiusi Scalo) Obviously, with a car, you would be able to make stops en-route (for example, in Pienza going to Montepulciano), as well as having much greater flexibility of not being tied to the bus schedules. If you do go by bus, avoid doing so on Sundays (except between Siena and Florence, and between Siena and Montalcino), since the frequency is much reduced (or none at all, such as to Pienza and Montepulciano). www.sitabus.it www.trainspa.it www.cpt.pisa.it (Colle Val d'Elsa/Volterra) www.ferroviedellostato.it

I just went to Siena for 2 days and used public transportation to go to other hill towns. Bus is definitely a better option than train to get out of Siena. However, you will need to study the bus schedule very carefully because while there are bus lines going to places, some schedules make a day trip almost impossible. For instance, there is a bus going to Pienza, but the earliest bus out from Siena is at 10:30 and the latest you can get back using a direct bus is 2:00. Considering it takes 45 minutes bus ride to get there, that really doesn't leave you much time to explore the town. These are the inconveniences you will encounter using the bus system.
If I could have spent more days in Siena, I would definitely rent a car.

For the reasons given by Dee (post immediately above), advice often given here is: take the train in places in Italy that are efficiently served by train, except a rental car gives the most flexibility and efficiency to explore the Tuscany and Umbria countryside and hilltowns.