Eric,
On the sponsorship front, I would focus on the Porsche brand value that the series has over say a Spec Miata series. Potential sponsors outside of the car parts world may be attracted to this such as higher end retailers.
Examples that come to mind are:
Sunglass Hut, Polo Ralph Lauren, and Tommy Hilfiger
Also, a contingency program is more of a win win for them because if they hand out a $100 gift card to the winner, the money all comes right back to their store. Unlike a tire contingency, there is a greater likelihood that the gift card holder is going to spend additional money in their store as well.
Other thoughts are following the lead of other series...and look at magazine publishers as title sponsors. Playboy is not very family friendly, but what about Automobile, Motortrend, Car and Driver, Cigar, GQ, Esquire...