well i think muppets from space had some problems like they had a directer that really didnt know what he was doing the story was good but i think it needed more kermit. It really did give gonzo more charictuer which was nice and it explained that long qustion what he was but he still now is a whatever. The cameos where lame to me thats the biggest problem i had with the movie plus it was at the time of swiching Frank Oz with Erick Jackabson, so there where not a lot of Franks muppets. Witch was really hard for some to take. Plus Brian Henson told i think it was Sony or the Directoer not to but the movie out in the big time summer run of movies that they do better off season, so that was a bit of a hurt for them numbers wise at the box-office. You can find out more at ign.com if i have the time ill look up that intervews of Frank and Brian henson about Muppets from Space and other things at that time going on with them and the muppets. i think it puts a lot of things into good view. heres the Brian henson interview
http://filmforce.ign.com/articles/035/035899p1.html
One more inside problem Muppets From Space had was that there where two versions of the movie written. One by Kirt T Thacher who know is a Muppet Director and the other version was written by Jerry Jull RIP. The one by Thacher was the one that was used for one reason or another. this was the beggingin of Jerry Jull pulling back from his work with the muppets here is that interviw
http://www.muppetcentral.com/articles/interviews/juhl1.shtml
He talks about some of the problems the Muppets where haveing at the time like the lack of the Kermit and Fozzie relationship and so forth i hope all this info helps with your qustions about Muppets From Space. take your time read what these great men have to say then maybe you can kind of tell why they have been a little leary of doing another big screen movie.