For a few years in the 1970s, Vivienne Westwood’s shop was the coolest place on the planet. The clock at this guerilla boutique still runs backwards, but London’s punk heyday is long over, and Westwood went from rebel to royalty. Never mind the bargains—her Anglomania label is a living museum, but it’s not cheap. Still, the fanciful couture inventions, flowing with fabric, are outlandish enough to enchant.