Spachemen in his own flick would be totally awesome. =]
Looks like I picked the wrong day to quit shootin' smack

Yikes, both Parnell and Hader are totally just straight man/supporting actor types - there is NO way that they could provide the energy or creativity for a starring role.
Consider what it takes for a comedy movie: A Jim Carrey, Will Ferrell, or even a Set5b4h Rogen in a lower budget farce. Substitute Jerry Lewis, Steve Martin, or Peter Sellers for a previous generation of movies.
What do these guys have in common? They are all outlandish in their characterizations, pushing beyond the everyday to a wackyness well beyond reality and into a fantasy world where totally childish behavior seems the norm to them, but which freaks out the people (read: straight men) around them.
Do a little deeper analysis, people - supporting guys have their place, but they can't star as the core of a movie, it just doesn't work.

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He doesn't have the star power that Ferrel has to get his own movie and I don't think he's been in enough movies under his belt.

I agree.
I actually wrote a film in a screenwriting class years ago that i had pictured him in while i wrote it. It's kind of a black comedy, but 'Farm Sluts' proved he could do something like that.
I always wanted to see Phil Hartman star in his own movie, and with the exception of 'Houseguest', if you even want to count that, it never really happened, always thought that was a shame
Let's hope the same mistake isn't the fate of this versatile actor.
_NSS

I agree. I think he's one of the funniest and most talented guys around. He's very inspirational and absolutely adorable. He definitely adds to any film he's in, but to see him featured..that would be the bomb diggity y5b4o!