Perhaps the most overlooked engine fueling inflation is the “wealth effect,” the extra spending from Americans feeling flush as their stock portfolios and home prices jumped by trillions during a tag-team, Olympic sprint for both. By far the biggest share of the extra outlays on the likes of new cars, home improvements, and laptops comes from America’s top income tiers. Besides opening their wallets as their net worth swelled, those high-earners—who own the most expensive houses—tapped the fast-rising value of their manses as ATM-style fonts for cash. The sudden spike in their nest eggs and their cash-out refis keep the...