We did this cruise last November and IMHO the cave tour in DR was awesome. A little scary at first as the entrance was guarded by a guy with a machine gun. The drive out there was also not too pleasant either. We drove though an area of the city which to me was just "Slums". MAYBE you might bypass this as we docked in a different port than normal.
We did the tour in Curacao of where they make the Curacao liquor. Recomendation, mix the chocolate sample with the coffe sample!
Aruba we de a sunset boat tour, nothing spectacular but the rum punch was free, and we had a really good time
Grand Cayman, I think we have been there 3 times now and always hit the Margaritaville there too