There's more than one class of judged cars. There's trailered concours, coucours driven, trailered modified, modified driven, occasionally driven, driven daily, etc. Each show has classes advertized and there is a class for almost any car state. Within limits, you choose the class you enter.
Let's jump right on to daily driven. This class can be any car that is driven frequently...undercarriages of daily drivers are not judged areas, open hood and open trunk are discouraged in this class (although one can open the hood and trunk and it does influence judges...you don't have to, and you won't get a deduct for not opening them), minor dings and scratches are not judged, etc. What judges look for in this class is general condition, character of maintenance, attention to safety, appeal, etc. Yes, you get a lot of deducts in this class but so do others competing in it. The fact is, if you enter enough shows, attend show and shines, and just be a good neighbor, club member, or whatever, you will win a trophy. My '98 V6 absolutely stock car has won two firsts for just being clean (and having a nice set of wheels and tires on it). I entered it only because my classic was not ready to be shown. You just never know what will happen until you try.