Personally, I don't know if tweens are ever going to go for them, given that most kids today don't.
Agreed, its just what kids are either used to or even remotely want nowdays - they'll certainly never be main Disney tween stars. They just aren't as relevant today as they once were, neither is Mickey Mouse, Fraggle Rock, Winnie The Pooh, My Little Pony, Smurfs etc. Some of those things can be redeveloped for the easier pre-school market (which thankfully doesn't really work with Muppets because they cant change the characters and the wit is a bit too sharp) or put out as one off films, or marketed the heck out of for a quick hit but they will never be the same. The only one thats been successful really are action hero type things and Transformers that they turned into an action movie. I think there is a chance the Muppets can be made a little more attractive to kids and also they can re-build up the family audience and do seasonal movies and TV shows that will get reasonable figures if promoted enough, but yes, i doubt even Disney think they will set the world on fire - they didnt even buy them for that. They just bought them for the distribution and licensing. So all that said, they're doing pretty well what with over a million people viewing a Beaker Youtube video.
As for Studio DC. I do think they are quite lucky to have been given the special (infact, a series of specials) and have these kid stars desperately trying to put them over - but the format just doesn't sit comfortable for them, it all looks awkward and the script especially seems a bit wooden ... at least from what we've seen. Maybe just doing a special one off TMS could have worked better and have been hyped as a classic thing but then kids don't know who they are, and it'd probably still seem out of place. I tend to think the only thing that could catch on is a sketch show on their own that was very well written and possibly get families to go see the movie (if there was a Disney teen in a supporting role). I always thought Americas Next Muppet on ABC was their best chance and they blew it, the format would have got people and the press's attention and if it was funny enough they might have got into it, stayed watching, voted.