Dover, I personally think this idea is great. Big ups to you for taking the initiative on this.
I'd suggest having the event in some parking lot near a restaurant where car people like to hang out - Hooters or Roosters, for example. (This versus having it like in just some random parking lot.) That would take care of people's needs for food, drinks, and restrooms.
I definitely like the idea of having some kind of entertainment there - a band or DJ or something. Music, drinks, and cars - I can dig that mix.
I especially like the idea of hiring off-duty CPD to moonlight as security. The more police the better, I say. Make it a very controlled event - if your going for improved public relations, the last thing you'd want is some retards making some antisocial spectacle at the event, you know?
Those are just my thoughts for now. Again, kudos to you for bringing this up.