Cancun, to drive, or to take a tour?

To be more precise, we'd be staying at Playa del Carmen (in an all-inclusive, based on past postings on this board). We're planning on about 2 day-trips, and 4 days of water sports/beach bumming. The first day-trip would be to Chichen Itza, and I am wondering whether we should drive or take a tour. We have 2 children in tow (aged 6 and 8), are not the most adventurous people, but would love not to sit on a bus for 3 hours one way if we can help it. Has anyone driven from Playa del Carmen to Chichen? Is it easy to find the way? How long does it take (It appears from the one single map I have that it is easier to go from Cancun to Chichen, than from Playa del Carmen)?

I cannot decide what to do for the 2nd day trip. Is Xcaret nice? I understand it's only 4 miles south of Playa del Carmen, but is it an interesting enough place to spend a day, with no sunscreen on (is sunscreen forbidden only for swimmers/snorkelers and divers or does the ban cover boaters and sight-seers)? Admission for this park is much higher than others ($60/pp or $100/pp for tour), is there really something special about it? I cannot tell from what literature I have on hand.

If Xcaret is not that special, any place else you'd suggest? Anywhere ecologically different but not too arid or too primitive for kids' sake?

Finally, nothing is more interesting to the children than colorful coral reefs teaming with fish. What's the best place for us to see these without great swimming/diving skills?

I'd greatly appreciate your suggestions!