Need for Speed: ProStreet Message Board  

The only thing they really matter for is if you're going to be playing online, and that could potentially get you banned.

The savegame I'm working on, the tuned cars, also made for online use.

As an aside, I'm going through career-mode as a side project, with ONLY 1 of each of the cheapest cars far each class, not using the AE86 either, because it is awesome car. And so far I'm kicking freakin booty. For career-mode it doesn't matter what car you have, the game automatically scales itself to match what you're driving. The only thing you will be doing by getting the best of the best cars for career mode is making it much harder to beat it - other than building up the cars you will use for online play.