Not to interrupt the trolljack ;-)
But wanted to comment on all the "change" concerns. I first went to Coz in the early '70's. Some amazing stuff to be seen, and a wonderful little town topside. And on the mainland, it was miles and miles of pristine beaches and Cancun was just a sleepy little fishing area that didn't even show up on the maps!
Next went back in the early '90's... do you think I saw some changes above and below the water line? And the quaint little town had seen its share of changes as well (the pod ships and party bars had discovered Coz). But on the mainland things were less changed (Playa was still full of dirt streets and the term "Riviera Maya" had not yet been coined, primarily because the beaches between Tulum and Cancun were still virtually untouched by big real estate developers.
In a few weeks I am headed back for the first time since then. Will I see major changes both above and below the water? Sure. But that's the nature of life! And it's what happens as we get older; if we are not careful we start living in the good ol days and whining about the current state of affairs.
Having had the blessing of being in many amazing places all over the world, I could whine for hours (don't even get me started about the Amazon rainforest, Oaxacan coast or the Hawaiian Islands), but what's the point? Things change. And I ascribe most of the damage not to hurricanes, but to people.
Personally, I am looking forward to the trip. Good diving, good food, wonderful people, and still a relative value when compared to most of the Caribbean.
As for the diving (and I primarily speak as one who rarely dives without a camera in hand), I am amazed that people don't find all sorts of fascinating things to look at underwater. As others have mentioned, the primary culprit is speed. When we slow down and look carefully, a whole new world opens up. If you find yourself with one of those fast-kicking dm's or groups, dump em. Immediately. They remind me of the rental horses that break into full gallops when its time to get back to the barn.
And even on a really bad day, there are all sorts of skills one can work on improving.
Enough (too much?) from me. I appreciate the conversation and look forward to sharing my input when I return.