BOSTON — Soon after Mitt Romney handed out eye-popping bonuses to top performers at his private equity firm in the early 1990s, a young employee invited him to ride in his brand-new toy — a $90,000 Porsche 911 Carrera.

Mr. Romney was entranced by the sleek, supercharged vehicle: at the end of a spin around downtown Boston, he turned to the employee, Marc Wolpow, and marveled, “Boy, I really wish I could have one of these things.”

Mr. Wolpow was dumbfounded. “You could have 12 of them,” he recalled thinking to himself.

But Mr. Romney had frequently driven an inexpensive, domestic stalwart that looked out of place in the company parking lot — a Chevrolet Caprice station wagon with red vinyl seats and a banged-up front end.

It was a stark sign of the tug of war, still evident in Mr. Romney’s life, between an instinctive, at times comical frugality, and an embrace of the lavish lifestyle that accompanied his swelling Wall Street fortune.