I don't know what the solution is but maybe the concours cars could be judged on a Saturday (I wouldn't think they would be involved in a bbq trip - then, maybe the judges might). They could then be put on display ALL day.
As I recall, at the Nationals that were held in Canberra, the concours cars were not 'locked' up at the beginning. We had just the judging area with the ramps fenced in. Perhaps one car on the ramp with another waiting at the approaches. I know they prefer to have the judges away from the entrants etc so that they can get on with their work. I recall back in 1994 at Penrith (my first Nationals (without a car)) there were entrants making comments to the judges.
Also, when I was leaving in the latter part of the afternoon I was speaking to one of the concourse judges who commented that he was having a look at the rest of the cars (Display Cars ). I said, "well you haven't got many to look at because most of them have left".
I think traditionally Friday was the day you travelled to the event, Saturday (for the concours cars) was cleaning day and Sunday judging day, Monday travellling home day.
I think when you look around at the days we were there you could see there were different groups. The absolute car shiners (the all dayers - more likely the concours cars and perhaps some Display Class cars), the party goers and car shiners (quick wash, rub down and grab a beer - ahh that sounds good) and then party goers (wash the car, have a beer and socialise). We are all different. However, I think you have to enjoy the whole thing with a happy mix of preparing the cars and socialising. I love catching up with people we have met over the years. Just love it.