We've done it twice. Once we had Fairy Godmother and the other time we had Alice. We'll be doing it for our third time next week...so we'll see who we get!
It's a nice relaxing experience and certainly worth it. My oldest thing they're too "cool" but they enjoyed it anway. There are also some photo spots in the theatre that even my older kids like goofing around with before and after the show.
It only takes about half an hour or so. I'd do it for sure.