The first thing to be said here is that whatever this person says it has to be believed because of his credentials - after all he is a share trader.
The second thing to be said here is that price increases above their capitalized value would not have occurred if " the incessant spending sprees " were done by private entities, that is, by private consumers and investors, as amply illustrated by the Roaring Twenties, which as you know occurred during the gold standard and were followed by the great depression.
The third thing to be said it that a regime of low interest rates has nothing to do with an increase in the appetite for riskier investments.
"The "Roaring Twenties" of the previous decade had been a time of industrial expansion in the U.S., and much of the profit had been invested in speculation, including in stocks. Many members of the public, disappointed by the low interest rates offered on their bank deposits, committed their relatively small sums to stockbrokers.
By 1929, the U.S. economy was showing signs of trouble; the agricultural sector was depressed due to overproduction and falling prices, forcing many farmers into debt, and consumer goods manufacturers also had unsellable output due to low wages and thus low purchasing power. Factory owners cut production and fired staff, reducing demand even further. Despite these trends, investors continued to buy shares in areas of the economy where output was declining and unemployment was increasing, so the purchase price of stocks greatly exceeded their real value."
