Of course you can go to a car show with a dirty car, they won't lock you up for it :lol:
I'll be heading there more or less straight from work after a quick change into my bike kit. It's about an hour from my work so I'm planning on heading away from here at about 4:45 to get there just before 6ish (i hear it all kicks off around 6 or just before), unless it's pissing down here when I'm about to leave