I don't think PM: The Thousand Year Door will be in limited quantities, I think the only reason the original was so hard to find was that the N64 was in the last year of its life, so Nintendo assumed not many copies would sell. It's a shame, because it was an awesome game.
As for the game being teh kiddiez... if your friends are too cool for anything but First Person Shooters and wrestling games, then yeah, you probably won't be bringing Paper Mario out for them to play. But if they're not too cool for Mario Kart, then they're not too cool for this either.
I'm jealous of you, Bill. I still can't find the game. *boo hoo*