Well, I think it's a combination of no. 1, 2 and 3
I myself never wash my belt because of the tradition, but if it gets really dirty and smelly, the hell with the tradition. It's just not dirty enough yet. I do wash my gi daily, though.
And as far as germs go, Colleen, I wouldn't worry so much about my belt germs in a dojo full of smelly feet when I have quite often to stick my sweaty face to these sweat covered mats when being pinned. Aikido is disgusting sometimes, no?