kdistler, I like your new plan.

We have gone directly to Florence from FCO more than once; it makes check in a bit easier and I do doze on the train.

Siena is a good day trip, as is Fiesole (a half day trip).

If you want to visit a winery from Florence, tripadvisor.com has a good list of companies or drivers that arrange that.

A very easy and very fascinated short trip from Rome is Ostia Antica. In fact, it's the best day out from Rome that I've ever taken.

I will keep the rain in mind and the alternate plan looks good! I will research more on those options.