We have not been to any of these ports and have never had any interest in a Caribbean cruise, but the price was so attractive that we decided it would be a relaxing vacation as winter starts to grip Canada. I can tell you what we are doing which may help you think about possibilities.
Costa Maya: There are a number of well-reviewed beach clubs fairly close to the port, but we decided on a more remote one 20-30 minutes south that is quieter and has snorkeling off the beach. Almaplena Eco Beach Resort, http://www.almaplenabeachresort.com/
Harvest Caye, Belize is an isla