Street parking should be priced such that approximately 15% of it remains empty. If the street is getting full of residents, then the price should go up. Until the point where it makes financial sense to build more parking or have less cars. If street parking cost even just $0.50/hour, it would make more sense to rent a car for the occasional weekend trip instead of keeping it on public land.

I would highly recommend The High Cost of Free Parking, which talks about this extensively.