I've never seen anything too disgusting in Noe Valley. The main principle of distribution of filth in San Francisco seems to be this: homeless people are too lazy to climb hills.
I lived near 30th and Noe (on Harper). Harper was clear. It was way up on a big hill. The bottom of the hill, 30th, Church, Dolores --- great Chinese food, filthy.
My point was, I lived in really crappy SF, I lived in hipster urban SF, and I lived in residential SF, and they were all filthy.
I found that observation a bit odd. The part about North Beach being clean was also a bit suspicious. Whenever people make blanket claims about how dirty SF is, I wonder if they've ever been to the western half of the city.
If Noe Valley is covered in poo, at least it's dog poo.