We plan to go to Chichen Itza but I don't think we will end up on the excursion offered through club med. There are a huge amout of tour operators in Cancun offering the tour on a daily basis (many for half the price). My friend came back from going on that tour and suggested that we try and get to the ruins before the mass of buses do.
We found that we could hire a driver to take us out there before the tour buses arrive (and when it is cooler...in the morning) for around the same price. The more people you book with, the more the price goes down per person (even less than the club med price when you book with 4 or more). Then we can ask the driver to stop if we want to eat someplace, stop in a small town, or take pictures, etc. Plus, we can pick any of the days to do it. At least that is our plan as of today.