TRANSFORMING an arresting-to-look-at coupe into an equally appealing convertible is not usually all that difficult. What can prove difficult is retaining the basic handling and performance qualities of the usually lighter, usually torsionally stronger coupe. The 350Z roadster scores well on both counts because, while it retains much of the coupe’s performance, it actually rides and handles better. And, apart from offering an open-air experience, it’s also more secure, with a small, but handily-shaped boot large enough to carry a golf bag. As a sports coupe, the 350Z does very nicely as a sports convertible, it arguably does even better.