Hi OZ1, welcome to Cruise-Chat! Congratulations on your upcoming cruise! The Solstice is a beauty. One of these days I'll have time to post some pictures of her. If you'll look a little further down the main page, you'll see our Caribbean Port Chat section. You can use the "Find" feature in the upper left hand corner and type in your ports. It will pull up all the posts made about them, and maybe you can find something that interests you.
We have done ship excursions and done excursions on our own. It just depends on what we are planning on doing. If you are comfortable with the port, you can usually do things for less on your own. However, some ports it's actually more cost effective to take the ship's excursions. Whatever you do, make sure you're back to the ship on time. They will leave you and it's up to you to catch up to the ship.
Best wishes and have a wonderful time!