Gold has gotten a bad rap. Long seen as the investment choice of the cranky and the fearful, the metal yields nothing; as Warren Buffett has said, it just “looks at you.” This year has been especially lackluster for gold. Its price has slumped 8%, to about $1,200 an ounce, and is off more than 35% from its high of $1,900 in 2011. Adding insult to injury, Vanguard will soon rechristen the largest gold-oriented U.S. mutual fund and shift its focus away from the metal. But this out-of-favor asset class now deserves a place in investment portfolios. Compared with stocks...