I went last Aug Bank Holiday and spent the entire day there. The track is good and you can walk all the way round. I could also get into the pits and take shots (if you ask nicely) of the cars in bits too, which added a different dynamic. The prices are reasonable too as well as car parking.
There are a lot of places that you can shoot from and a lot with long lead ins to help you track cars early. Turns 1 and the Esses bends are probably your best chance.
Depending on the day, it became a little repeatative as there were a number of rounds when the same cars were racing, so by lunchtime, I had got most of them already but you can never predict the crashes!
I had a 5d2 and my 70-300 lens and had a right day of it, some of the work is on my website. I also got a shot of one car, that when it was published on social media, the driver noted it and learnt something about the handling of his car. Another like the shot so much he purchased a framed print from it.
