Unfortunately, if you are brushing your teeth, you are not really making progress. You are just slowing down the decay of the status quo. So if you reward yourself with points for brushing teeth, you are still kidding yourself.

On the other hand, maybe a game with decaying experience points would be a good idea. If you don't do anything, you lose experience - evil. Could be gamers wouldn't like it, or else it would have been tried.