I have 4 sons, we went to GWL last winter when they were ages 3, 5, 8, and 10. My kids had a blast both at the water park, and with the magic wand thing. We went the year before when they were 2, 4, 7, and 9--but I think my youngest was too young to fully appreciate it at that point. There were a few slides he was too small for, etc. We only stayed one night, and really only did the water park and magiQuest thing--we didn't go to their arcade, spend any time in the gift shop, etc.
I can see us continuing to go to GWL for at least a few more years, probably by the time my oldest is 12-13 he won't be as enthusiastic about it.
As for "things for adults"--we didn't even bother visiting the spa. We saw it strictly as a "for the kids" stay. HTH
