We saw this back in (I think) 2005, when it came. It was a nice big promotion for the Happiest Celebration on Earth. Basically, the Incredibles take a vacation to the Magic Kingdom at WDW, but Syndrome attacks and madness ensues. Just think: murderous Small World dolls. We really liked the show and how they brought several of the attractions to life on the ice. The Haunted Mansion sequence was pretty cool, and I think they also had a Pirates portion that was pretty good.
The Disney on Ice shows are always fun for a good "Disney kick" between theme park trips. The skating is always supurb and the shows are a lot of fun. As far as things to buy: Yes, there is TON of stuff available to buy. Sno-cones come in plastic glasses shaped like characters. They've got programs, dolls, light-up toys, plushes, Barbie-type dolls. You name it, they have it for sale. If you're bringing kids, be prepared to say 'no' a lot, or bring a big wad of cash to shell out for the goodies. They're inescapable.
Enjoy the show. You'll have a great time!