Earlier quoted context omitted.
A 1950's upper middle class lifestyle involved owning a relatively large house, and sane working hours with in many cases only one wage earner. It's simply false that you can live this way today on the same dollar amount.
Even in among the lower middle class lifestyles, you'd have exactly the same minus the "relatively large house". However, if you go back 50 years earlier, the lower class lifestyle was not that different from the favella living in slums around the world, where entire families lived in one or two rooms and everyone in the family who was able was responsible for contributing to making ends meet.
Your second point (which I agree with) seems to imply that the US standard of living peaked in the 50's