I think the main difference is in the level of detail. A show car looks good, but to prepare a car to concours national level is another ballgame. Most big concours competitions, porsche, ferrari etc have split street, meister classes but you find cars that should be in a meister class in a street class as the owner thinks he has a better chance of lifting a cup! very naughty. At top level originality is king, although again ive seen straight out of bodyshop take the honours. When i used to judge i always awarded more points to a original car. Also rich if we had wind of a street car being trailered to an event, then out of the event they would go!