Simon,

Give www.mybeachboard.com a look. Full of members that travel to MX on a regular basis...many have been going for years. Lots of info; friendly folks.

Since you like off the beaten path, take a look at the Akumal Bay area. It's south of Playa and has some of the better snorkeling in MX. I heard the area was hit pretty hard by the hurricane but should be fine by next year. Craig in WI has vacationed there for many years and you might find his posts interesting...has a recent trip report up, with pics.