Your second point (which I agree with) seems to imply that the US standard of living peaked in the 50's
The lower bound on lower middle class is, according to Wikipedia, $32,500. There are plenty of houses available for purchase in the $60,000 range, which is well inside of affordability ranges.
There are a plethora of rural homes available within those ranges, but that level of income isn't necessarily exclusionary to city dwelling either. Dallas, San Antonio, Cleveland, Cincinnati, St. Louis, Tampa, etc., are all very affordable, and at least according to MSN[1], has homes available for less than the lower bound on lower middle class.
[1] - http://realestate.msn.com/what-you-must-earn-to-buy-a-home-i...
> The lower middle classes can't own any house at all with just one wage earner
is not a true statement. If you'd like to qualify it further, feel free. I suspect I'd have to research more to answer, and I don't necessarily disagree with the sentiment you're suggesting, but presenting falsities as facts doesn't do any argument any particular good.
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.