I'm not sure you really followed my suggestion. I said they should charge for parking while validating parking for paying guests (i.e., someone with a receipt from one of the resident businesses). If you could show you were there to spend money, your parking would be free. This is a very common thing in larger cities. The only people it would discourage from coming to DTD are people who just want to walk around (i.e., people Disney doesn't really want there in the first place).
I'm not positive, but I believe the lot at Disneyland's Downtown Disney is already a pay lot. It's really not that wild of an idea, and it would solve Disney's problem of free-loaders in the DTD lot without forcing anyone without a car who wants to finish off the night at Magic Kingdom after seeing Cirque de Soleil or Disneyquest to factor in an extra 30 minutes just to wait around for a bus at a hotel they have no interest in visiting to begin with.
The only real objection I've ever heard to this is that it would back up traffic to get out of the lot. There are ways to get around that. I recall one particular idea from slappy magoo a while back that would have receipt reading computers set up at regular intervals along the sidewalks, so people could easily validate their parking before they ever got to their cars.