Aw, but I ♥ Bailey. He's had speaking roles ever since Season 1 (even though they're mostly generic butler lines), so it's not like he was shoehorned in like the other extras. Wally, on the other hand... I would really like to see a George episode that didn't also have Wally in it.
If anything, I wouldn't mind it if they included some of the characters' extended relatives, if only for an episode. They've introduced a lot of Francine's family over the years- her grandfather in "Background Blues", Bubbie in "Is that Kosher?" They've even made Joshua Redman Francine's uncle, for whatever reason.
Another thing- did anyone notice how in the "Arthur" parody cartoon that Arthur and D.W. were watching (I believe it was in the Mei Lin episode), the Arthur-looking character was named Alfred? I thought it was supposed to be Andy, as in "Andy and Company." At least that was the name of the cartoon in the episode "The Contest." Goes to show you that the writers don't pay attention to details in their own show.