Just got back from 5 day to Cozumel and Playa del Carmen (Calica).Having done both 4 and 5 day trips down there, I'd change to the 5. The 4 just isn't enough time. Anyway to your question.
We did the Xcaret park at Playa. (you realize Calica is just the dock, most everything is in Playa?) Xcaret is mostly a nature park. The float through the "underground river" is fun, the park well maintained (for Mexico). You can see Manatees, dolphins, leopards and other wildlife. It was fun though I'm not sure worth $49. It sort of depends on what you are looking for.
We did the Fury Catamaran snorkeling adventure in Cozumel. It is fun and a great party It is not good snorkeling. You get maybe 30 minutes in a pretty confined area, so you are constantly bumping into other people. The coral we saw was dead or dying though there were lots of fish. On the boat it's all you can drink. Some people take full advantage of that. The crew is friendly and keeps the "party" going. Like I said it is a fun party. If you have snorkeled much before you may be disappointed in that part of it.
Have a great trip!