Geneva’s 73rd Salon International de I’Auto has hosted the debut of many of the world’s great cars. But seldom have so many of them been relevant to the North American marketplace. The count is usually five or six; this year, at least a dozen new concepts and production models impact what we’ll eventually see or drive over here. Besides OEM reveals by Lamborghini, Porsche, Ferrari (“First,” April 2003), Mercedes-Benz, and Saab, to name a few, the boutique design and production houses use Geneva to strut their always-interesting stuff: Pininfarina, Italdesign, Bertone, and others. If there was any star of the show, it was Audi, which showed a new A3 (coming here), a dazzling concept car called Nuvolari (said to portend a future luxocoupe model), and, indirectly, the Lamborghini Gallardo, as…