My children have done it, DS9 and DD4 at the time, and they said that it was fun. The only suggestion that I have is it depends on when you go. The first time that we booked it (1st of Dec. 2002), it was cancelled because of the weather, too cold. The last time (end of Dec. 2004), again because it was too cold in their opinion, it was moved inside the GF. They did the scavenger hunt in the hotel and my children said that it wasn't as much fun as they think it would have been had they been able to go on the boat.
If you are going at a time when the weather is nicer, I think that is worth the money. They did allow us to get our money back if we decided not to do the inside hunt, since they had cancelled the boat trip. My children decided that they would give it a try anyway and after decided that it was ok, just not as good as they had heard about.