RealmMan;164522
I just thought of a corollary: Family Matters.

Stick with me, here.

Both FM and RGB had an annoying pest (with a grating voice) as a minor character – Steve Urkel and Slimer, respectively – who was quickly promoted from minor/recurring to series lead… and in both cases, eventually brought the show down.

I have to disagree with part of your reasoning with Family Matters. Not Saying Urkel had nothing to do with that show's downfall…I just think there is more to it than that. Back when Urkel was introduced his antics only really affected the “child” cast of the show; this made the character cute and lovable. Unfortunately, like the children in the show, he grew up and his antics became less cute and more annoying. Less Lovable and more loathsome.

JamesCGamora;164523
I have to disagree with part of your reasoning with Family Matters. Not Saying Urkel had nothing to do with that show's downfall…I just think there is more to it than that. Back when Urkel was introduced his antics only really affected the “child” cast of the show; this made the character cute and lovable. Unfortunately, like the children in the show, he grew up and his antics became less cute and more annoying. Less Lovable and more loathsome.

One could argue Slimer “grew up” as well. Note that he was decidedly baby-ish early on, then “matured” to Dennis-the-Menace level–young enough to get in/cause trouble, but old enough to recognize it.