I think one of the things about overdone skits is that it might have more to do with the audience members than the performers.
I only go to three cons a year, so I see, on average, about 100 skits a year. I don't look up skits on youtube. Aside from some yaoi themes and several sailormoon and naruto skits, the 'problem' of overdone skits doesn't really apply to me.
This year at AMA was the first Avenue Q skit I've ever seen ^_^ and it was fantastic ^_^
Am I in the minority? Is it partly the audience members attempting to see and critique as many skits as possible that makes skits seem overdone? Don't get me wrong, I've seen terrible skits, but it wasn't because they were 'overdone'.
"Mommy is tired honey, she just wishes the cosplay fairy would come along and finish all the hakama."
--A response from me to my son ^_^;;