If you check that page and the following one in the same thread I think you'll get an idea.
I think it's worth it. I don't particularly like Nurburgring, but I'm loving the 430 Scuderia and all the other cars are fun to drive (and I rememberyou even like the 550 and 575 cars, so you won't have any problem with the 599 and 612 )
For 5 pounds you get many more hours of "new" things to do/cars to try, so I guess it's good value for money.