It's hard to say, I picked one of my favorite articles for the MAD vault. Which is one of the features of the Magazine so they don't have to actually pay artists or writers to come up with new stuff.
I decided that I wanted to be a voice on every animated cartoon in the history of the world - even shows that haven't been on the air for a very long time, that's going to be harder to pull off.
In fact, when I come up with an idea for a parody I try to resist the urge to Google the idea to see if someone has done it already because the answer is almost always, "Yes, of course they have, they've thought of it!"