Mega Mike,
I liked your postcard. Already told you it looks good overall. Take the "hug me" jacket out of the drivers side window; I think you got a good promo piece.
FYI: You may be able to find that glossy paper at your local print shop also. I carried a little bit in my shop for years. It does make for a classy look. Layout of the pics and info is also important. Look at promo pieces from the NASCAR, SPRINT, and INDY Car folks. The focus is usually on the car. Can't miss those sponsor decals in the pics.
Don't be put off by people telling you NO Thanks. That is the worst that can happen! Nobody is going to take away your birthday, or anything. You've only hit up a few; Your just getting started. Win a couple of races, maybe they will be calling you! Of course, the price just went up a bit.
It's an advertising venture for the prospective sponsor. It's deductable at tax time. Park your car in front of their business; People WILL STOP!!! They may not need their product, or services, right at that time; but they WILL REMEMBER where they saw the cool race car! Race fans are more likely to visit a business that sponsors a race car. It's something they can identify with. As with other forms of advertising, the prospective sponsor needs to be made aware of the long term benefits of sponsoring your car.
Guess that's all I have for now on the subject.
Best Of Luck To Everyone Seeking Sponsorship!!!
Steve