I'm not sure who's likely to know this, but I'll give it a go.
From 18-31 August I was on holiday driving around Europe, on the 25th we were meant to be going toward Stuttgart, but I noticed on the map that we could make a very small detour and visit the 'Ring. We parked in one of the car parks and I could instantly tell that there was something going on, the cars were too loud to be public. I went to ask if there was somewhere we could see the track from, and was told that it was the testing day for a race weekend, and we'd have to buy a ticket. Screw that, we went to find some food, and it just so happens that not only does the cafe have a view of the start/finish straight, but it has an outside stand that you can sit in and watch the cars go by. We stayed for about half an hour, then headed off.
It looks like a great circuit, I'm definitely going to head back in future for a longer look (and a drive round). It's very unnerving to be on a public road, and see cars fly past at 150+mph on the other side of a hedge.
The cars seemed to be a complete mixture. From old and new Porsches and tuned up BMWs and Mercs to Jap cars like NSXs and S2000s, there was even a Vauxhall (Opel) Zafira going round! Couldn't tell if they were on the large or small circuit, I'm afraid.