A few ideas of what they could have had Walter say, regarding minor characters....
While bringing the gang back together, Walter could have suggested picking up Thog next.
Or, if the scene with "Mahna Mahna" playing on the radio wasn't cut, it could have inspired Walter to suggest locating Mahna Mahna and the Snowths next.
Or, after Kermit claims they got everybody but the others point out they didn't get Miss Piggy back, Walter could have pointed out "We've also forgotten Lew Zealand, Wayne and Wanda, Link Hogthrob, Bobby Benson's Baby Band...."
It is also interesting that Walter doesn't get to interract with any Muppet lesser (in character importance and popularity) than Scooter. The only ones he interracts with directly are Kermit, Fozzie, Gonzo, Miss Piggy, and Scooter. I don't think he even interracts with Animal or any of the other new Muppets in the film.
And I feel they should have brought Sweetums, Thog, and The Mutations out into the crowd in the finale, dancing with the big crowd of human extras (though the Mutations aren't there in the finale). Sweetums and Thog's pressence in the finale is pretty much treated the same as any regular-sized Muppet puppet.