We were there in May.
We did the meet and greet service. Seemed to save a lot of time, especially on the way out (Saturday), but as others have said, YMMV.
We dove with Living the Dream. FANTASTIC experience. Everyone there was wonderful. We finished certification while there so our dive boat experience is limited, but the boats were great. The service was some of the best we've had in any industry. Talk to Liz and see if you can arrange a Kittiwake dive on one of your mornings... we did one while there and it was a great experience, both the superstructure and swimming through the decks.
We did Stingray City with Captain Marvin. This crew was great as well and the experience was fantastic, would certainly do again. We did the 3 event thing with snorkeling, Stingray City and Starfish Point... Stingray City was the highlight (of that day) by a large margin. There is a place online where you can check the cruise ship schedules for Grand Cayman... see if you can book Stingray City on a day with few or no cruise boats in port... it gets very congested.
We rented a car. Would certainly suggest this as others have said. Had a somewhat bad experience with AVIS, and the Immigration guide said he thinks they are the worst of the group. If you do rent, a drive out to Rum Point was fun, and you can do Starfish Point while you're there if you want.
The Turtle Farm was nice for a short trip... We did not do the snorkeling while there but if you like sea turtles, there are a lot to see. The rest of it was not great.
Supposedly the dolphin encounter by the turtle farm is pretty good, as long as you are not bothered by the ethics of captive dolphins or the ridiculously overpriced (optional) photo packages.
Hibiscus Spa at the Westin was fantastic.
As for restaurants, we went to Macabuca on BBQ night (Mondays), which was a nice buffet style dinner and probably the best value of our meals there. It is right next door to Cracked Conch. Our favorite restaurant was Calypso Grill... will certainly go back next time.
While we didn't do it this time, Living the Dream (and others) offer guided night shore dives from Macabuca. Something you could do if your wife wanted to wait at the Tiki Bar, and you could have dinner right after.
Have fun! We really enjoyed our time there and can't wait to go back.