Just thought I'd check in with my post-trip report:
The merchandise selection was very dissapointing. The shop right outside the MuppetVision theater had some stuff, but not a whole lot (only 5 different adult t-shirts, for example).
A few other shops in MGM had Muppet merchandise, most significantly the shop in the backlot tour. However nothing that couldn't be found in the theater shop.
But that aside, the MuppetVision show was fantastic! The pre-show was different than I remember, and it looks like they've made some small changes to the theater too (for anyone who goes, pay very close attention to all the little details -- there's laughs to be found in every nook and cranny!)
Oh yes, and I found the hidden Kermie!