We booked our excursion through Disney. We did eat on the island. If I remember right, choices were a hamburger or hotdog, chips, drink, and maybe a cookie. Not a buffet lunch, but it was okay.
We spent all the time we wanted snorkeling with the sting rays. There was a specific time we fed them and they also offered pictures with them. We had already moved to the beach area when the next boat came with the cruisers from Carnival for their excursion.
My daughter and I had plenty of time to clean up and then go shopping in Nassau when we got back. I thought it was definately worth the money we paid.