I mean, this whole tangent started because of the baseball episode, so I both kinda agree and disagree with this. Something like "Krusty Gets Kancelled" lives and dies with celebrity cameos, and it's one of the all-time greats. Plus that Baldwin one was pretty weird in how the celebrity guests were in, like, the entire episode as themselves. I can think of the Mel Gibson one like that, too, but most of the later season episodes I've seen that have celebrity voices still tend to use them for just cameos; there's just no joke beyond, like you said, "it's this famous person!" Later writers just didn't have as good a handle on the whole "celebrities playing themselves" thing. Like, the celebrity shows up, and then a character on the show has to comment on who they are; that's usually a sign it's a bad era.