Do you mean tracks or cars? I haven't heard mention of premium and standard tracks too. And I think the weather has been confirmed already according to those new E3 clips.
There's been a few videos of GT5 demos that show certain tracks as premium. One of them being Circuit de la Sarthe ( vid here @ 30 seconds )
I think the Nurburgring circuit was listed somewhere as premium as well, but I don't know of any video/screenshot showing a standard circuit. Anyway, by having the distinction, there must be some difference between the two.
The weather systems I would reckon far from being in yet. I consider the black spots at the start of the E3 trailer just a visual design blurb, and the cloud shadows passing over the field a hint at weather at most.
Wether they actually implement it is still vague, and how even more so. Dynamic generated / pre-set before race / race line drying up after traffic / night time temperature fall influences on motor performance / etc. Mostly hoping/dreaming so far. 👍