We went a couple of years ago and wouldn't do it again. It's an afternoon trip and you have to take a ferry out there, if I remember right we waited for about 1/2 hour each way. The food was ok (open beer was nice) but after about an hour you've done it all. We felt a little trapped to be honest. The snorkeling was decent, but we saw much nicer sights snorkeling at Arashi beach and Boca Catalina (free).
To sum up, it's very very touristy. Some people like that, some people don't, but not worth the time or the money IMO.
We didn't do the sea trek thing, but we disliked just about everything about DePalm island. The snorkeling area was so crowded when we were there that people were constantly running into each other. There were some impressively large parrot fish, but that isn't enough for me to go back.