In regards to the bumpiness:
Keep in mind that your viewpoint is as if there is a camera that is solidly-fixed on the frame of the car, not from the bouncing eyeball perspective of the driver. (Without a cockpit as a referece like GTR, this is the way it should be)
Home video hand held-cameras on the `ring are going to show a lot of vibration because the person's hand is shaking. In-car footage from a camera fixed to a roll cage or something will show the drivers body shaking and their head moving elastically from bumps in the car, but those movements are exagerated when compared to the car's actual roll and pitch.
For example, watch the on-board cameras carefully next time you are watching the TV coverage of an F1 race or Le Mans. The driver's head, which is where the sensation of bumpiness would be felt in real life, moves around quite a bit, but when you focus on the horizon in the distance as a reference for car-body motion (which is OUR reference in a video game, not the sensation of our head being tossed around) you will see that sizable bumps and jars produce a relatively subtle visual change.
The biggest effect will be seen in external replays with suspension travel, and from the drivers perspective, be felt in forcefeedback and in the driving dynamics of varying traction as the suspension is under compression and rebound. As long as the camera axis is slaved to the chassis (again, as it should be without a full proper cockpit), the visual representation of track bumpiness won't be as severe as we would expect.
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