I noticed you are from Canada, so am I, We just got back from the Western Caribbean on the Paradise (Jan.11) It was fabulous (nice to get away from the cold here!!)
I booked an excursion for Cave tubing through Reggies. If you do some research, there are a lot of positive reviews from him. It is considerably cheaper than booking it on the ship. We booked it with 3 other couples and that was it!! We had our own private tour, while the people on the ship had groups of 50 or more!!! We paid $65 each, and the ship charged $85-$100!!
I would highly recommend Reggie!!
As far as the other ports we visited, Roaton we went snorkelling, took a taxi to the west side beach, very cheap as we had our own snorkel gear. In Cayman DDO the stingray city. If you can book with Sosos cruises, it is only $24, but they left early on their tours, so they were unable to accomodate us, so we went with Captain Marvin, again we were fortunate to go with only 2 other couples we had met on the ship and again got a private tour!! It was really neat and cost $34. We also went snorkelling with them.
If you have any questions, feel free to email me and I'll help you out!!
Best of luck