Why don't you give Aqua Cat Cruises a try?
Scuba Diving Bahamas Liveaboard Aqua Cat Cruises - I'm not sure how much your wife wants to be able to do while on board but if she's laid back enough she might like it. I've not done AquaCat, so take this with a grain of salt. BUT.....from hearing from many people and also seeing a few cruise videos of their's, I've gotten the impression it could be good for divers and non-divers alike...
Now, AquaCat is a liveaboard dive boat - so there will primarily be scuba divers on board. But they cruise in and out of Nassau so your first day and last day of the trip you'll get to do the resturant and casino thing and during the week you'll cruise the Exumas. The diving appears to be the best in the Bahamas. You can get up to five dives a day in but when not diving you can relax on the boat or take a shore excursion. They have a skiff called "Sea Dog" that takes people ashore to beach comb, relax, picnic, kayak, and snorkel. Unlike other liveaboards that pretty much don't do that many shore excursions this might be to your liking and your wife's. One of their shore excursions gives you the opportunity to interact with a colony of Rock Iguanas - I think there's only a few colonies in the world - so that's something to look forward to.
If you really have the funds and want to think out of the box there is a dive destination with frequent and interesting shore excursions, what about the Galapagos Aggressor or Peter Hughes Sky Dancer? It is pretty much the priceiest that liveaboard trips get (short of Antarctica) but maybe it would be a trip neither of you would EVER forget!
I hope these ideas are of some help to the both of you. I think I know what you're getting at with cruises - I am very much turned off at the idea of a cruise ship. Give me ample diving and no crowds and I'm a happy camper. I know cruises are fun, everything is right there for you, and also I've never done one - BUT...I'm confident I'd find it too boring - too much like life at home (all the creature comforts) and not enough diving.
For non-divers I've heard that if they're laid back and not itinerary driven and like the idea of having basically their own private yacht for the week with good food and small groups they end up liking it even more. AND, the AquaCat does discover scuba and cert courses, perhaps without coercing her, your wife might get curious and want to try scuba diving out. But if not, the shallow dives would probably be great for snorkeling as well as the shore excursions. Check it out and let me know, I'd be curious to know what you decide.