Well, I think all of the cars will look good based on what I read from the quote I replied about; obviously, not all of them will be of a high Premium quality. First of all, every car can be used in Photo Mode/Travel, and all cars will be customizable. At the start, only spoilers could be added, and then, with the Spec 2.02 update, closer to 100% of GT5's cars were given the ability to change their wheels, instead of only the Premium cars having that ability). I'm making the presumption of all cars being customizable means that they'll need to have greater (exterior) detail them look weird when they're customized and using those once "Standard" cars in Photo Mode where the LoD was at a noticeably higher level and the imperfections easier to see (EVEN with the Premium models).
Right đź‘Ť. That's what I think it's going to be like and that's what I took from Kaz's answer. Basically, there will be three levels of quality in the cars. Fully detailed cars that are new to the series will especially not have the problem of being "under detailed" (the Veyron was first introduced in GT PSP so that says something about new cars to future GT's all being fully detailed from now on) along with GT5's Premiums, then there will be cars that are "good enough" compared to the greater detailed, full HD cars and the third level will be decent-looking, but not terrible.
Kaz states that not all cars will have the extent of detail that the Premiums had in GT5 (maybe meaning that they simply won't have detailed interiors) and he ambiguously states that there will be cars that won't have interiors that are completely modeled by saying "not all cars will be made fully 'Premiumized" (which I think means that the exterior detail will be improved enough for parts to be fitted onto the unknown number of those cars but will range from having simplified interiors to no interiors modeled at all). He didn't say that there would be some Standard cars that will stay the same and not be updated.
I actually said, "The second part of that underlined sentence is a telling sign that all cars will look good (meaning much more closer in their LoD, or more balanced out, in comparison to the way all cars were modeled in GT5 1.0)." I think you misread what I intended to describe, but iainoflo85 clarified that for me.
From another thread, SlyckTires also explains it better than me about how I said Standard cars' exteriors looked like they've been drawn using MS Paint.
Spoilers are an extension to the cars (which is why those were possible to add from the beginning pre-updates and likely easier) whereas wheels have to be fitted precisely to each car to look normal with higher detail/polygon count (the stock wheels weren't of good quality until they visually improved after the Spec 2.02 update) whilst naturally moving in relation to the suspension's settings and behavior. A similar idea applies to the carbon fiber hoods and body parts.