If you've never been to a port, never stay on the ship. At least explore it. One port that one person may hate, the other person may love. If you've never been, you never know.
We'll be going to those ports this yr. Not sure what we'll do in Ochos Rios, but Grand Caymans, snorkeling is a must!
Keep asking for ideas of what to do. I'm sure you will find something that will interest you. You can also ask on Carnival board too if you haven't already.
Which ship are you going on?