I think most of the US is going back to underpowered vehicles mainly because of the fact that most areas are so congested, horsepower means nothing, so people are moving to MPG.
It is also the fact that oil has kept the economy's growth stagnant for so long. Things pick up, gas prices rise. Prices go up, fees on airlines go up. The economy stagnants, and oil falls a little bit due to demand. In fact, our oil usage is less than it was in 1997, but at 3-5x the prices.
So unless something changes, I expect a repeat of the 1970s -- underpowered vehicles will be the norm, not the exception because people value MPG over vroom, vroom.
There are some differences. Engines now have "enough" horsepower to be able to get places without being too obnoxiously slow. Even in the 1990s, one had to eat breakdown lane if someone was trying to merge with a Mazda Protege, Dodge Shadow, or a compact car. Now, even the ratty VWs that the college students drive have enough get up and go to get to highway speeds.
After 2008, the US has changed fundamentally. The weenie engine cars that were snickered at in the past are now the rage.