First off-if you are sailing out of Miami it is very nice to come in at least the day before and stay in South Beach or at least plan a day here. A Caribbean vacation without starting in South Beach just isn't the same to us-we live in Florida and STILL feel like we are on vacation in another country when visiting SOBE. And the port is only a 10 minute drive from Ocean/Collins ave.
One thing I think about Miami is the ship excursions are always crappy. The Everglades one is an okay idea if you want to spend time boating around a swamp on your tropical vacation-otherwise you are best to just get off and do your own thing.
Miami Beach is one of the best beaches-it's a nice place to spend a day. Also our favorite thing to do in Miami is sit in one of the outside restaurants on Ocean Ave and people watch. You can see celebrities, wackos, you name it-all sorts of people. And get the GIGANTIC 2 for 1 drinks. Just be prepared that anything in SOBE is going to COST you!