If you are into water activities which it appears you are then the Caymans are the way to go. Cabo's beaches are mediocre and unless you are into deep sea fishing or just sitting around a pool, I would skip it. Las Ventanas is fabulous in Cabo, but also starts at $575 per night + 10% service charge and 10% tax. On the other hand, your rooms are cheaper in CI but your meals and drinks are pricey($12 pina coladas and $19 hamburgers). CI is clean pretty with great water.

I would also look at alternative islands in the caribbean. Perahps Belize or Virgin Gorda or even St. Johns, they all are known for incredible water, beautiful beaches (exceptBelize which is more scuba) and small elegant hotels. Unlike CI where the hotels are 2-300 room factories where you will share your honeymoon with 1000 strangers. I would look for a little more elegance and seclusion. Free advice, and you know what thats worth.

Regardless, enjoy your time and congrats.