Normally, when a resource is scarce, we let the market set its price. So why not do the same with parking? That's what the city of San Francisco has decided to to, because it is populated with geniuses who own iPads and still manage to get a tan. By using “demand pricing” — in which the price of a parking spot reflects what time of day it is and how many people might want it — unnecessary or extended stays in parking spots are discouraged.
The idea isn't merely that only rich people should be allowed to park on public streets — though that's potentially one of the effects this uncharacteristically Ayn Randian policy. More importantly, cruising for parking spots can constitute up to 40 percent of traffic in some neighborhoods, which makes commuting slower for everyone, and fills the air with noxious chemicals that make kids dumber and more asthmatic. So if we discourage cruising by making parking expensive, we might end up with a generation of kids who are smart enough to ride bikes instead in the first place.
City Attempts to Find "The Right Price for Parking", Planetizen.