The reason I see precious metals coming back, is that the whole idea of fiat currency seems to be closly linked with cheap energy. As energy peaks, fiat currency will peak.
When huge supplies of cheap energy were discovered, in the form of crude oil gushing out of the earth all through the first half of the 20th century, massive economic and population expansion was possible - but only with a concurrent expansion of capital. With the gold standard basically keeping the money supply fixed, capital could not rise along with the new energy supplies. With abandonment of the gold standard, and the innovation of endlessly expandable fiat currency, the means of global civilization's recent hyperbolic expansion arrived. Continuing this thought, it seems to me that most of the problems of the past century were actually caused because monetary expansion could be accomplished simply by decree, but energy expansion was not quite so simple. So in many times and places, there have been shortages of energy (either political or geological), but any government could increase currency supply at will.