The kids in the sage program here (gifted/talented) go to Astro-camp every year. Not sure if it's exactly the same thing, but probably similar.
My DD absolutely LOVED it. I didn't let her go as a 5th grader as I thought it would be more special to have her wait and go in 6th grade. I didn't think she needed to go more than once. I wish now I had let her go both years.
They did do a lot of team building activites which may not be quite the same if you are not attending as a group. All the kids I've talked to about it said it was a great experience. Our sage teacher is very picky about the programs the kids participate in - he would not take them back year after year if it was not a worthwhile experience.