High Definition television can be picked up for free using your dear old grandfather's rooftop TV antenna. People will figure that one out very soon when they realize they can maybe live without cable TV. A similar thing could happen with terrestrial radio, and if the powers that be could just be progressive enough to take a fresh look at the AM and FM frequency spectrum, they might find something that is profitable.
HD radio tries to squeeze itself into the unused sidebands of a broadcast frequency. What would happen if HD had access to the entire frequency block(both sides plus carrier) or if HD could span a few consolidated adjacent blocks? A hell of a lot more usable signal could pass through. The antennas on cars are already designed to pick up those frequencies. All you would have to do is change out the receiver. What are you going to use it for? I don't know. Test it out anyway and then let the market figure out a use. Let's stop being so short sighted.