I am also considering a "new pre-owned car. I looked at the G35, and because of the styling/look, it was one of the top on my list. However, one of the major problems that I read about while checking them out was the tire wear issue. I didn't read all of the posts, so I don't know if anyone has mentioned it, or said they had a problem with it personally. But, from what I read on some review forums, due to the engine weight and the suspension set up, the front tires can wear very unevenly on the inside tread. This results in cupping in the tires and many people have had to replace tires once a year since they have owned the car. This can be a minor issue in some, but other have reported it being a big deal. Just something to consider when looking at them. So, pay attention to the tread when test driving. If you want to keep quality tires on it, this problem could end up costing you upwards of $800 a year, excluding other maintenance.
Oh, and according to dealerships, there is nothing they can do to fix the problem.
*EDIT* The tire problem is reported in the G35 Coupe, sorry for the misunderstanding.
You may also consider the BMW 3 series, Acura TL, Audi A4, and the Lexus IS (a bit more price wise). They are all around the same price used, being a couple years old with around 20-30k miles.
Hope this helps.