The new Chrysler Crossfire, a stylish, sexy little coupe, will almost certainly match or exceed its modest sales targets. It may also put a slight dent in the sales of the Audi TT, Honda S2000, Porsche Boxster, BMW Z4, Alfa Romeo GTV Spider, and Nissan 350Z. But the new two-seater, very much a Mercedes SLK in disguise, has a secondary and much more important role, writes Neil Winton.