Thanks for sharing the article.
I'm no economist, so I have little educated opinion to offer. I do agree that things are different right now, but that in itself is not really different. Meaning, there have always been differing, unprecedented combinations of economic/global challenges being faced at the time -- inflation, deflation, unemployment, oil shortages, wars, sector bubbles, etc. I don't see the markets as overvalued when I consider the recent highs in the context of where they were about 5 years ago -- basically where they are now. I'm in it for the long haul -- I have a strong confidence in the U.S. markets and U.S. companies in general. That said, I'm not particularly aggressive either; I probably have only about 30% of my overall net worth in the stock market.
I have far more concern over the ability of the large Wall Street investment firms to (legally) manipulate markets in ways they were never able to before. Things like the derivatives debacle, for example, and other junk that was sold to mainstream investors while all the big guys got rich, tanked the markets, and then ran away with the money. There don't seem to be any hindrances to Wall Street being able to do it all over again. "Too big to fail" is just as bad or worse now than it was in 2008 -- has even one large bank or investment firm been broken up?