I usually recommend you get some Z friends or experienced car-show goers, or a Z club, and give everyone paper & pencil to write own things you should look into (relative to your model, class or goal, NOT their idea of a "show car") and you later go through the sheets to see if you did miss something that should be looked into. Things like "needs a bigger stereo or video screens" would not be appropriate for a stock class 240Z, but might be for a super-modified 350Z, but all those eyes going over the car should probably catch at least several things you didn't, even if you should throw those ideas off the final list. I suppose you could use a judge's critique from a local, "A.M.M.Y." judged car show, but I really wonder if those kinds of judges know what's what on your specific car/model, unless all they are about is cleanliness.