Standards to be in GT6?? Meh, couldn't give a monkeys.
I had the most fun on GT5 in standard cars, mainly the FGT, the tank car and the Alfa 156 touring car.
Gran turismo is after all a driving simulator, you don't drive a car by looking at it wishing you could take some pretty pictures or fit a spoiler. I buy the games to drive the cars, if the models are slightly dodgy and pixelated, I'm not bothered.
If I can't fit some aero parts so what? As long as I can race the car to my hearts content, either on my own or against some friends then I will be happy. Provided the physics and tyre modelling etc are decent of course.