it possibly didn't sell as dealers find it hard to shift big expensive fuel drinking v6's in this current climate, and with all the snow, who wants to buy a rear wheel drive car.
if all seems sound and the gearbox is in good nick, the only thing i would be tempted with is to compression test the engine, if its got a full nissan service on the right times etc, then it should be alright.
the 350z has very few engine problems as long as its well looked after.