I think the 'American Dream' is a bit of a moving target.

No doubt, as we became richer in a material sense. Still, there are at least two aspects of "the Dream" that have been fairly constant over the last 100 years, even as the details have changed: personal transportation and greater living space. The first provides the freedom to travel where and when you want to, rather than being subject to schedules set by others, and the second is enough space so that you don't have to listen to the screaming brat in the family "next door". TTBOMK, every developing economy, as it becomes richer, immediately begins spending money on personal transportation and larger living spaces. As one example, consider China's real estate boom and staggering forecasts for automobile sales.

To the extent that they are required to give those things up, the American public as a whole will feel that their standard of living is declining. The interesting question -- at least as far as I'm concerned -- is whether all or part of the US can maintain these "critical" aspects of their standard of living in the future. I suspect that, for example, the strip along the east side of the Rockies can manage. There are plenty of local energy resources, adequate water (with a bit better planning than now done), reasonable food production capacity. I hold out much less hope for the BoWash corridor, regardless of the higher density of its metro areas. There are not sufficient local resources to support the 70M or so people living there.