Pisa is a nice easy airport, and the city is worth at least a day or two of your time. Last spring I stayed in Pisa for a few days and rented a car (easy to do at the airport, obviously, but there's also a Europcar office right in town, by the river) to take day trips to Lucca and San Gimignano. There's a good bus system in that area, too, if you don't feel like driving.