I think we could take a page or two from a boxer's training manual. I'm thinking about the use of focus pads and belly pads for developing speed, combinations and accuracy. Not that your dojo doesn't already employ such methods already, just karate dojo in general.
I've heard and actually made similar comments along the lines "it doesn't have to look good as long as it works" This because I have trained a number of inexplicably ugly (technique) but none the less effective karateka. This thread asks a great question though.
That scruffy yet effective fighter is only going to be more effective with improved accuracy, precision, focus and body positioning. It's a little like big men who don't use hip & body movement to full effect because they don't have to. Doesn't mean they wouldn't benefit immensely from it.
Great thread GJEC, I'll be putting a little renewed pressure on those few "sloppy but effective" students.