making a good and accurate collision of the meshes is probably not the easiest thing, and in the end, it would probably just be like a safe zone around a character position that no one walk through or up against, this wouldn't be like real collisions in my eyes and I'd rather have it as it is now.
Ofcourse this is is arguable depending on how hard it is to make and how well it would represent real collisions, but my guesses it wont be that good.