It does seem more logical to put similar cars together, not only does it look tidy but means you stand less chance of missing something.A bit like shopping really ,you dont want to find some electrical goods with the fruit and veg or the toothpaste next to the bleach .
I don't go to that many shows but its always nice being parked next to something of a similar vintage even if its just to make a better looking photograph .The Ivan hirst show was a nice example i thought .