Yes, I have and it's quite disappointing. Most shows nowadays are looking for the most outrageous custom fabs. Greatest number of screens (I saw one car with screens in the headlight assemblies). They're looking for bigger and bigger wheels (the Dub show wouldn't allow my car in the show because my 84s, wire wheels, were only 20"). They're looking for $20K paint jobs and chrome undercarriages and engine bays. Bottom for the big shows throw $100K at a $1000 old school (not even a classic or antique) and never drive it again - you may get into the show.
As for the smaller neighborhood/local shows bring a damn good, simple demo (or as I do - a remote controller and a convertible) so you can get as much explained in the shortest amount of time. Maybe you'll get an honorable mention. A CarPC falls under the category of interior customization, you still have to show under the hood, the trunk, and have a flashy body & wheels. And to make matters worse, interior can be as little as 20% of your overall score in most shows.
I just cringed whenever I showed my car cause the kids and adults alike would drool all over the car with 15 screens from a 32" to numerous 5" and all they were used for was DVDs and Playstations. After my demo, the adults had a better understanding of a CarPC, but the kids just liked my joystick shifter. What a sham, oops ,shame. As far as judging goes, my PC might as well have been a chrome Endelbrock intake.