Definately worth doing in a group! We used to do the track evenings occasionally, they were good, we had about 10 bikes out one night just mobbing the novice group
It's a very good idea, if you don't have some sort of backup ie a van, to take a spare set of levers btw. I rode mine home after a 70mph off one time, all it needed thanks to the crash bungs was a new front brake lever. You see an awful lot of people standing stuck and worried in the pits because of little things like this.