It's a shame the Muppets and FR are now ruled by 2 different companies ... because the Muppets could have helped provide some links to FR.
Since the best "plot" we have so far is "Fraggles in Outer Space", it's hard to know the best way to market it. Putting out the DVDs helps give us some background, but the general public won't be getting those. There needs to be a way to increase general interest. Despite what anyone feels about Bayformers, I think they got it right in dragging the rest of the public into the theaters. X-Men did a good job too, with those "Mutants are real" kind of things where we got to see Sen. Kelly's political ads and stuff.
I would imagine we'd need to set up Outer Space first, introducing the idea that all this time there has been another world with weird critters in it. Hype up the nostalgia-escapism factor. Have spots with differently-aged humans (so it doesn't just come off as a kid thing), each with their own different "issue" (like a lonely kid in a playground or a frazzled office worker). Have a Fraggle hole dramatically open up in a wall, out pops out Gobo or somebody, cheers up the human and offers them some fun down in Fraggle Rock.
After spots like those have been playing ahwile, do some ad parodies. Do some "insurance" ads courtesy of Boober or the Firefighters. Have Gobo and Red play sports in "Gatorade" spoofs (maybe with "Is the magic in you?"-type tag lines). Have Junior advertise some gardening equipment. Have Uncle Matt show up in random "real" commercials in the background or even commenting on the products/services. None of the products would be real, of course ... they'd all be spoofs ... but they'd get the attention they need.
Follow this up with a web site like the new Muppet one with all the really hilarious blog-type stuff and games and such.
This way, any re-casting doesn't have to seem like absolute blasphemy, as fans already know who's dead/retired and the general public wouldn't care anyway. It'd also give the new voices time to stretch their chops before the movie comes out. Put the ad parodies with shows whose creators are big-time hard-core Muppet fans ... maybe it'll be cheaper that way ;D . And for God's sake, if the movie comes out, have a follow-up project. Whether it's a new show or a continued Web presence or whatnot, don't just drop it after the movie. FR can still be milked plenty ... take advantage of it.