In GT5, I could replace the body code of standard car like R34 GTR Vspec with premium body code R34, and no one would know when driving it
Looks premium, but the codes/parts that made the car is all standard R34
What really affects the car is suspension and chassis codes, suspension codes can be very specific to each car, so different model years like R34 GTR '99, '00, '02 may have different parameters inside the suspension codes ( ride height range, spring rate range, dampers, ARB ) but also could be the same (exact same)
So, it's not because the quality of the visual model, but the codes that made the car.