One thing I really learned from our recent trip to Rome, Assisi and Florence is that we decided early on not to try to do too many cities in one 10 day trip. Because we wanted to have an enriched cultural experience, we stayed three days in Rome, one day/overnight in Assisi and four days in Florence (two days were travel days from the US to Italy and back again). We actually planned to do a day trip to Sienna but Florence had so much we wanted to see and experience at a reasonably relaxed pace that we ended up skipping Sienna.
Another thing we missed was the countryside except as it passed by while traveling by train. So our next dream trip will be Tuscany and the Amalfi Coast.