Key West is an interesting port for a morning visit, which we had.
We experienced it as a quaint town to walk around and made interesting stops at the lighthouse museum and the Hemingway House. We took pictures at the southernmost tip of the United States.
To really get the feel of the town I think I would rather have driven the highway from Miami and stayed a night or two.
Wasn't really impressed with Cozumel as a destination overall. We signed up for the Mexican Cooking lesson and that was excellent. Chef Oscar had the 20 or so guests cook a three course meal that was served to us on completion. He kept us entertained through the experience using his skills as a chef and a musical entertainer. My impression is everyone thought similarly to us. The taxi van ride to and from the resort was a harrowing experience. The driver noticed we were nervous and talking about his driving so he nicely turned up the music so he could no longer hear us.