Scaling games like Grim Fandango should be quite possible(and probably will be if Residual is ever finished), it's not much harder to scale a 640x480 flat image than a polygon model. The trouble in doing so is making screen coordinates match up with the game scripts I guess. Everything would be messed up if you were to simply scale up the whole thing, but I'm no expert. Hopefully one day it will be possible.
I think it's more likely that we'll see a GF:SE before that happens though