Part of a cruise is when the boat is docked at the island(s), you're not on the boat for 3 solid days. You can do shore excursions (anything from snorkeling to ?? - I've never been on a Disney ship so I can't speak specifically). You can also go shopping or explore the island on your own. The only thing I would be concerned about is if there is a full day at sea (which I doubt there is on a 3 day cruise, but I could be wrong). You'd be on the boat the entire day. However I'm sure Disney has plenty of stuff to keep you entertained.
You say that your wife accepts your Disney fanatacism (sp?) and she's ok w/ going to Disney for you honeymoon. A large part of marriage is compromise and I personally think that you should do the cruise as well since that's something she really wants to do.
Just my 2 cents!
Lori