@Brenden - About half of the mods I make to webparts and their modules are behavioral, the other half are simply changing the structure of the their markup to move some divs around (or get rid of those nasty table layouts). Like I said, they do the job they need to do, but their markup is ugly, so I inevitably wind up cloning a webpart just to change its appearance because I don't have time to design a more decoupled solution at work.
@Vrigil - Very cool. That is totally something I would contribute to. I'll set this idea aside for awhile and see what happens :)