There are lots of people on this cruise chatting at a Cruise Critics area. There's been discussion of tours. If you're not familiar with that, you might want to go and see what's been discussed. They're even getting everyone together for a special cocktail party. Here's the link to it:
Somewhere there is a link to the 8/30 Golden Transatlantic sailing -- part 5 is the most current, but you can look back into parts 4, 3, 2, 1 and see what was discussed.
As for myself, since I've been to Venice, Florence, and Naples, I don't need to be so ambitious with touring these cities as if this were my first visit there. There is just tons to see in Florence -- museums, churches, etc. Naples has Pompeii which is spectacular, but being I've been there and done that, I'm opting for the Amalfi coast drive to Ravello and Positano. (Sorrento and Capri are beautiful in case you want to check that out.)
Good luck with your decision! So many things to choose from!