Trying to visit Pisa and Lucca as a day trip from Florence is a bit hectic. Trying to visit Siena (which merits a whole day by itself) and San Gimignano is even more so. Then throwing in a day trip to the Cinque Terre, and trying to "see" Florence in a day and a half, and it just is too, too much.
I wouldn't go to the Cinque Terre unless I could spend at least two nights. I've been there twice for the day, once when we were staying in the Maremma area, and once when we were visiting Elba. Both times, which were both in the off season, the towns were way too crowded for my comfort level. I've heard that the crowds are mostly day trippers, so if I could spend at least two nights, I'd have a chance to to see the towns when they're not sinking under the weight of tourists, and also time to do a little hiking on some of the less frequented trails. I'm pretty sure that on a day trip, you'd be sticking to the more crowded trails. However, since I've never spent a night there, I am saying this based on hearsay. I just know I wouldn't be interested in a day trip from Florence.