I did several laps at the Ring last year, early october, about 40- 45 deg F, light to medium rain, foggy... It was about one of the coolest driving experiences I've ever had, it was just prototypical Nurburgring weather and lots of fun...
But I would that even though I have done hundreds of laps of the PS2 version of the Ring, it was virtually no help whatsoever to learn the track once I was there. Nothing can convey the vertical relief of the place, the amazing steepness of the hills, and how incredibly tight and narrow the track is. Just about every other corner has a blind apex or exit. The grip level is a little strange, it feels like it has pretty good grip, and for some reason it feels like the grip is pretty good even in the rain, and does not seem to have the property of letting go suddenly, it seems more forgiving for some reason. But that's the only thing that is forgiving about it, runoff area pretty much everywhere is minimal.
That said, I agree with Greg that I would go into debt to do some races there in the Grune Holle...