I did my OW certification in Grand Cayman, got 7 dives in total, though of those you listed only the kittiwake. I thought it was pretty cool, more experienced divers may have a different opinion. I went to stingray city but i didn't dive, at the spot i went to the water was really shallow, a pretty large group of people (several boats) but it was cool, worth going to, not sure if the diving it is worth it (you go to a different spot, nearby I'm assuming)... I dove with Ambassador Divers the whole time (did the stingray city trip with them too) i think they do snorkeling too... I did a night dive from shore at turtle reef too which was pretty cool.. turtle farm is, well a turtle farm, so they eat a portion of those turtles, some are released, i guess it depends on you if its worth it (wasn't a bad experience wasn't great)
---wanted to add that my experience with ambassador divers was great, they were knowledgeable about sea life and alert able to point things out i would definitely have missed w/o them (including an octopus on the night dive)