I think we have 5 levels.
Garbage bin (Audi Auto Union)
Standard (GT4 stuff)
Standard+ (Toyota SOARER, Mitsubishi Lancer Evolution VI ´9, Shelby Series 1,Pontiac Sunfire etc...)
Premium without interior (RUF ,R390 road car, etc)
Premium (GT5P, and GT5 stuff).
My opinion on the re-worked cars is that PD had a goal of getting some of them in better shape for GT6 and had a minimum level of tough ups they needed to get done before release. This is what we are seeing. Now I'm sure they didn't stop there and are continuing to work on them and we will probably see them as premium models in the near future.
I was feeling so good about the updates done to the standards and then I see that Supra.. I'm just speechless.. how can PD continue to release in game assets that look like THAT?? The standards in GT5 were quite bad but now with more cars getting updated these jaggy, straight from the PS2 era are sticking out like a sore thumb, they have to stop releasing PS2 era models.. this is getting crazy! Oh well back to admiring the updated cars!