Hey, your superman ascent while diving looked great. Remember to keep exhaling!!
When I was last on Isla Mujeres, we rented a golf cart and traveled most of the same path you did. It was nice to see things outside of their downtown area. I definitely recommend going south... turtle farm, Playa Tiberon, and Punta Sur. And, yes, when on the carts, warn your backwards facing companions of upcoming topes - they still hurt as much, but at least you know when to expect them!
Thanks for the excellent trip report and photos.