I'm a die hard GT fan, but IMO the reward system, and several other aspects of this game, are sorely ill-thought out. In GT4 I would do the same championship over and over because there were multiple cars that you could win and they were all cool and fun to use race cars, touring cars, etc. - I wanted to collect them all and enjoy using them. In GT5, I think they got too caught up with the novelty of some cars and didn't consider that nobody wants to put in 40 minutes of time for a championship in pro or expert with a race car only to find out at the end that the single prize car is a $40,000 base car. That's ridiculous, and I'm down for saving up $$ but at the price of the good cars - $1,000,000+, and the fact that they almost all are unavailable by any means other than getting lucky in the used car dealership, I pretty much won't ever get the chance to enjoy half the cars in this game that I was really excited to see on the car list pre-release.
I'll do this, but it's because I want to enjoy the cars, and PD painted itself into a corner with this - people will do whatever they can to get cars because the system is ridiculous.