That would be a pretty good idea, a parody of the game.
With parodies, a good thing to capitilize on is the faults in the game and exaggeration of the character's personalities. The hard part with Psychonauts is that they were already wacky.
And absolutely no inside jokes. Those always ruin parodies.
EDIT: When Raz meets Boyd we could have a joke where Boyd is making perfect sense, pleading to be let off the island but Raz is convinced he's insane.
Sounds more gruesome when I type it out.