In areas with very little mass transportation such as FL, suburban NJ, HI, etc. where nearly everyone is coming in with a car, they should just build the cost of parking into the room rate and be done with it. I was unpleasantly surprised to read that Marriott Marco Island just imposed a parking fee- I'll bet the Hilton down the street just did the same thing. Parking at the Hilton was free when my husband and I were there a year ago.
In urban areas, many people get a shuttle or taxi to the hotel and do business within walking distance or via public transportation. Those are also areas where land is extraordinarily expensive so there's a big cost to setting aside parking space. In those cases, I can understand that the people who use the service should pay for it (although I've seen some exorbitant parking fees- JW Marriott in DC comes to mind).
I agree that free parking would be a great Elite perk.