Thanks everyone, very helpful tips. Great pictures @bonsai3s. Yes, my wife and I have been to Rome. Spent 2 weeks there for our honeymoon in 2011, including a trip to Capri. The plan is 4 nights in Rome pre cruise, for nostalgia. 5 nights in Florence post cruise.
After all these comments and looking at pictures of Acropolis, I think I'll get off at every port, and get back on the ship early in a couple places. I do enjoy ancient history. That's too bad Santorini is that congested, however I feel like I need to see it, as it might be my only opportunity. The ship is in Santorini 13 hours, 7am-8pm. Hopefully that's enough time to explore Oia and get good pictures.
On the "explore itinerary" tab when I booked it said Mykonos is tendered. You're saying it's not? That's good news, probably will explore on my own, without an excursion there.