I think this is probably one of the things the government can do that is unambiguously good and will touch the lives of many, many Americans. It's also an example of a market failure where there is no market for the product or service demanded. It's a textbook example of the tragedy of the commons where the gain on the TV signal is owned by no one and thus not protected. It seems like a perfect thing for the governing bodies of the country to spend time on if that's what it takes to get it done.
I do not buy your theory that this is pandering for votes. I doubt very many people will chose their elected representatives based on this issue. Instead, I think that is just a convenient rhetorical device by which you are discounting the value of this measure.
> Going further, what's the positive national interest in encouraging Americans to watch yet more broadcast television?
Personally I don't think it's in the national interest for the government to decide for its citizens what they ought to be doing with their time. Instead, it should observe what the citizens wish to do and, where appropriate and efficient, facilitate those activities.