When Gwyneth Paltrow paraded more than $25,000 of designer gear at her eight-day ski crash trial last month, there wasn’t a double G, interlocking C or Medusa head logo in sight. Instead, the Goop founder donned a series of understated luxury looks in salubrious shades of bone broth and protein powder. Enter the era of stealth-wealth dressing, where “Buy high, look low-key” is the philosophy. Classic shapes, subtle detailing, muted colors and the finest materials are assets, while flashy...