Look closely at your brochure. Playa del Carmen is a short stop to disembark those people who are on a scheduled tour. Those not on a scheduled tour stay aboard the ship for the 12 miles or so to the port of Cozumel.
I don't think XCaRET is good to do on your own. If you do you will have to do it form Cozumel which is possible because I checked a few years ago but it was just as high or higher than the ship. In this case I'd do the ship tour. But look at the times - I think the dolphin deal at Xcaret was only certain times and when I checked we would not be there for it. Debbie