So we can live in reasonably priced and comfortably sized spaces without cultural or income sacrifices.

Right now density is as you describe > a metric for progress. But that's old fashioned. Living in a $3,000 closet in SF or NYC in a building with 100 other closets shouldn't have to be a near-requirement to work for an exciting company or enjoy your time off in an exciting place.

I like to think this modern world has enough intelligence to improve our antiquated and slow modes of transportation. We've done it for communication.