Thanks to Marginal Revolution for pointing me to Donald Shoup's The High Cost of Free Parking, "a detailed, economically insightful, data-rich, and lengthy, impassioned plea for charging people for parking spaces." MR also includes a link to a in-depth (13 page) review of the book by Dan Klein.

This may seem like a narrow issue, but Sharp figures that our parking policies amount to a subsidy to parking costing well over $100 billion each year. This system not only encourages Americans to drive cars at the expense of other transportation options, but directly encourages urban sprawl.

This statement from the review neatly summarizes the problem:

“Planners set off-street parking requirements because the government fails to charge fair-market prices for curb parking, not because the market fails to provide enough off-street parking” (498).

I've always thought that parking subsidies were one of those government policies that helped the (relatively) wealthy at the expense of the poor.