Thanks much for the ideas.
I think I will look further into a day trip to Coz from Cancun. I don't think I can pull off an overnight trip but I don't mind a long day or an early start to the day. I will have to look into the wreck you mentioned, I hadn't run across that one in my research.
My wife and I are both fairly experienced divers (I have over 300 dives, she has about 200), although only a few in the last year and a half since our daughter was born. We have been to Belize, Roatan, Maui, Kauai, Bonaire, Fiji, Thailand, and a lot in California (where we live), but never Mexico.