Interesting topic. I got in 2 dives on a cruise stop at GC many years ago, later did a Cayman Aggressor IV trip with 5 dives at GC, 18 at LC and 2 at CB (both at the Keith Tibbetts wreck). Here's how considering a Grand Cayman trip looks to me.
1.) If I want the reputed 'best scuba diving in the Caribbean,' Little Cayman gets the nod by reputation, with Cayman Brac a very close 2nd but averaging deeper dives. If I'm going alone, it'd make sense to hit one of those, maybe CB because I don't have much experience with it. I hear GC's east end diving with Ocean Frontiers is also very good, but it's well away from Georgetown, so if I'm going rustic for great diving...why not just hit LC or CB?
2.) Cayman Brac has shore diving, an edge over LC, but traveling alone I doubt I'd be adventurous enough to explore and take advantage of it, as it seems like a 'road less traveled' thing.
3.) Grand Cayman looks good for a 'scuba diving trip disguised as a family vacation' (wife's term), in that I could do a couple of boat dives in the morning, then spend time with family. As a cruise port, it's got topside excursions. But GC has a rep. for being expensive.
4.) A key resentment I have toward GC is it seems that, despite there being no law against it, most dive op.s prohibit solo diving. A key way to get around total trip cost while racking up dives would be to do solo shore dives to supplement the expensive boat diving, but that's not an option. Some people may come back with the sentiment 'It's their island.' Yeah, and it's my money and choice.
5.) I've got some GC dives, so it's not something I need to cross off the bucket list.
6.) If I did a family trip, Cobalt Coast is too expensive. With the kid, I'd probably be looking at Comfort Suites or Sunshine Suites, as at least in the past they seemed to be the value/budget leaders on 7 Mile Beach from the reports I saw. I'd also consider a condo., if it had good access to shore diving.
In a nutshell, Grand Cayman looks like a good option for a family trip, but pricy, bizarrely opposed to solo diving which I'd need to take advantage of the shore diving that's one of its advantages, and the diving is overshadowed by LC and CB.
Curacao has some similar 'selling points,' and has grudgingly gotten a little more solo diving friendly in places.
So I'm interested but not 'sold' as yet.