I'll do the cruise-ins mostly - and there are several each week within 25 or so miles. I'll also do smaller local shows plus two big ones. Usually car shows for me is just a place to park while I wander the rest of the show. I will return back to the car regularly, but wont stay more then a few minutes and that's just to check on it. As far as prep and contrivances - I only make sure the car is as clean as possible(it always is) plus print off my fact sheet of major parts as someone always asks what something is - and since CRS set in many years ago, drag that out if I can't remember.
There is one thing that does gripe me - a gathering of a bunch of folks right at the back of the car (often 2-3 cars) that are so close that you have to walk through or into their group to look at those cars. I wont. While I don't have any problem with these people gathering, just move away a bit so spectators can take a good look at your cars without breaking into that group.
Mirrors and ramps - this usually says to me that the person is thinking "I have LOTS of money and and PAID this big buck shop many dollars to build my car and now I want to show off" plus it conveys an 'attitude'. And is often a trailer queen car.