We went to Sea World last time because my DD (then all but 3) loves animals and we thought it would be neat for her.
We enjoyed some of the things, but overall felt that it wasn't worth it as there wasn't too much there that interested us. The shows we wanted to see were so close together that we couldn't see 1 without missing part of if not all of another.
I think part of our issue might have been poor preperation. We knew we were going for a day but didn't take the time to plan that day at all, so our first 30 minutes inside the park was debating what we want to see and how to make it work.
Overall I feel that if it's your first time there then it's worth it to check it out for a day, maybe two if it interests you more than it does my family. Otherwise I wouldn't see much of a reason to go back. We decided that we would only go back if we had another child who hasn't seen it. I would love to try the Discovery Cove portion, but there's no way we could afford it.