I'm not following how we end up in the same place. Society is richer in 2014 than it was in 1964; was richer in 1964 than it was in 1914; was richer in 1914 than it was in 1864; etc etc. Distribution of the "relative" pie may have changed, but we're all better off now than ever before.
A few things. You are basically talking a century or so of economic expansion in which supply/demand was a nationally (sometimes regionally) determined. Capital was largely immovable so workers had security. I would argue that life for the poor--urban and rural--was horrid at a number of junctures prior to the advent of greater government assistance to the indigent. The former elements of these items have eroded dramatically over the past 20 years and that has caused greater consternation among workers, especially those in service industries, and the latter is under attack.
I think it's also important to point out that government intervention in individual economic decision-making has helped fund the boom. The home mortgage deduction fueled the housing market after World War II and continues to fuel it today, as it's largely the major piece of wealth for most Americans (if one can afford a house). Social Security and other income maintenance programs have allowed senior citizens to remain heavy consumers. Whether or not that is right or wrong (or good or bad policy), the government sending out money to average Americans to spend does help the demand side of the economy. Investments in national defense have fueled research/development and manufacturing.
The growth in consumer credit has also played a role in how we may look better off than we actually are.
I think we are at a critical juncture when looking at these issues. The 20th century was the American Century because as people left farming and moved to the cities, there were opportunities ready and waiting for those workers in manufacturing and other industries. The system was relatively closed. Given our economy is now based more on services than goods (at least in terms of overall middle class employment), it makes economic security harder to attain because when capital consists of a bunch of computers in an office building as opposed to a foundry, it's a lot easier to move. Globalization provides cheaper goods, but it also erodes long term earning potential for a large part of the workforce.
I don't think I'm unduly pessimistic, but I think the new normal is going to consist of much slower economic growth and a much wider distribution of economic benefit. In other words, a continuation of the angst we've seen since 2008. You have to remember that a century is only 100 years out of all time and the conditions that allowed the American Century may not be extendable indefinitely. Economics isn't a law in the sense that gravity is, but it can come pretty close.