Hard to advise you if you should go to Florence. It's not like there's not alot to see in Rome <G>
If you do choose to visit Florence for a day, most of the "highlights" are located in a few block area... with the Uffizi Gallery, the Academia, and the famed Pontevechhio all within a few blocks of each other. You can reserve tour space/time in advance at Uffuzi and Academia... which I would advise so you don't waste too much time in lines.
Jill and Larry...For the last couple of years, because of aging parents and business concerns I cruise with a satellite phone. Bought it before " world cell phones" became more common. But the advantage to it, over cell phones, is I can call from anywhere in the world, as long as I'm outside. So, even on sea days... if I'm sitting on the balcony, I can call and check in if I feel the need.
My sister returns today from an eastern med cruise, and they rented a "world phone". After I talk to her, I'll let you know her thoughts on if they found it useful.