“Desperate Housewives” star Marcia Cross has been spotted shopping for expensive art at Miami’s Art Basel, but she’s also been doing the rounds on the party scene. Cross joined a well-dressed crowd at Valentino and Interview magazine’s cocktail party on the rooftop of The Webster boutique Wednesday, where she mingled with guests including Owen Wilson, Nicole Miller, Martha Stewart, Peter Brant, DJ Chelsea Leyland and Interview editor-in-chief Stephen Mooallem.