Every time I purchase a vehicle, used or new, I make it a point to clay bar it (3M), then apply at least 3 coats of wax (Meguiars NXT Tech Wax). I do that every 3 to 6 months after that, depending on how much the vehicle is driven. It's a pain in the @ss but it really protects your finish.
Man, stock 350Zs are really in dire need of wheel spacers.