Steve,
I think come the summer months this could be quite easy to get 10 people min on a Wednesday or Friday night.
I know I could bring 2 paying people, plus another 2 easily (Racing whores

) and I'm sure a few more stragglers would come. Head to the pub next door afterwards for a beer and food at dusk

.
I know its subject to weather etc but it could work. 7.00pm would be better for us travellers

. Perhaps you guys can sort some provisional dates and create a sign up?.
http://www.new-age.co.uk/sun-times.htm May to August 'could' work.
However, open track from 6.30pm till 9.30pm for a £10 or so would be wicked IMHO. Great chance to test some set ups in a relaxed atmosphere.
Neil