Is it just me, or is Christopher Guest's Waiting for Guffman pretty much the same movie as his later For Your Consideration? They're both about a group of marginally talented people - Parker Posey, Catherine O'Hara, etc. - who are trying to put on an unexceptional piece of entertainment when it's disrupted by an unwarranted bit of outside attention. In Guffman, it's a talent scout from New York, while in For it's rumors of Oscar buzz.
There are significant differences, beginning with the fact that Guffman is funny. Since Guffman is about ordinary people, we're much more willing to root for them than the peripheral Hollywood actors in For. The minor characters in Guffman are more indelible, especially David Cross and the too-little-seen Linda Kash as Eugene Levy's wife. And while it's ridiculous to think that some sort of talent agent would descend on a community-theater show in small-town Missouri, that might actually be more realistic than the notion that a Hollywood film would start to get some Oscar talk while it was still being shot.
Still, both films benefit greatly from the presence of Parker Posey. I don't think I've seen a bad movie with Parker Posey in it, although that's probably more of a testament to the number of movies I've seen.