Have a great time! Since there will be four of us (the other three are in their 80s), I decided the car would be worth it rather than a train. But you're right, with two, a train might just be better.
We will drive to La Spezia and then take the train into the Cinque Terre. A friend of mine is going to pick me up for a night soccer game in Bologna and I'll train back - and, conveniently, meet the seniors at the Florence train station, so that will work out well not having to drive to or in Florence.
The rest, we'll probably drive to -- Viareggio has what looks to be a fabulous Carnavale on Sundays in Feb. We're definitely going to hit that, and will probably drive to and from. We do plan on taking the tram up to Montecatini Alto. For some of the other "maybe" towns, Lucca, Pistoia, Prato, we'll play it by ear as far as driving or by train.
Years ago my boyfriend and rented a car in Tuscany for a couple days, and it worked well with him driving and me as the navigator, but traffic in the cities was ridiculous and I don't want to do that again!
I'll look forward to your updates. Make a point to have gelato at least twice a day.