I did found some Fact...
If the car is "roof-less", that will call you some old 3D memories.
Most modeling quality are much as PC game 8 year ago standard!
There cockpit view model are different with the external view models.
PD have put a several details.
Some example,
Common :wild shield is more polygon. Steering wheel are provided and not a shared models (even their texture are Low res.)
Toyota 7: The side gas covers(?) are doesn't like external models just a two pieces of plane there!
Most GT4 Le Mens Prototype : you may say "awesome why didn't apply in GT4 ?"
F2007 (Portable Garage Version): WHAT THE HELL THE STEERING WHEEL FROM PREMIUM F2007 ?
Caterham Seven : I pretty sure the mirrors frame is high polygon models!
in cases.... roof-ness Standard car are disappointed ... yeah... they are high polygon... but they are only dark cockpit without Bonnet and wipers ...
Also... in rainy situation,a ton of rain drops will stuck on wild screen for a while, and you have no Wipers to let the screen clear....
Sometime you will love GT PSP solution just place a camera inside the car models.