Well, ignoring these "hilarious" negative comments,
I'd have to say why not. I would actually love to be able to keep clean for +speechcraft.
I don't think we should suffer negatives for not washing (unless there are options), but we should get a bonus for washing. I don't see what the problem is with it. I guess it's because doesn't involving bashing monsters.
Hold on...so, being "cleaner" should get you a bonus, but being "dirtier" shouldn't have any negative effect? What gives with that? If you're going to implement this, then in all seriousness "basic cleanliness" should get you your base speechcraft (or whatever Skyrim equivalent is implemented) rating, being very clean and well-dressed gets you a bonus, and being filthy should indeed have some sort of negative consequences.
Of course for this to work believably, it would somehow have to be modified based on who you're speaking to- a nobleman holding court would probably have less tolerance for someone who was "less than spotless" than a sweaty woodcutter halfway through his workday.