since you state you will be giving them away at car shows I like your idea of having people in the background. To me it states you are one of them, part of the crowd, sociable, that kind of thing. I think the "thank you " on back also contributes to that feeling I get, but I would leave the thank you off. But that's just me.
Also I would do a mock up of the back in blue instead of black to see how that looks. Everything seems to be in black lately. I am bored with it.
I think in your third post you said you were new to doing this but you have probably already thought of this: go to Walmart and get a print made for 30 cents to get an idea of how it will look when done.