I like the idea of an organised car show, with an organised run out to may be to GBS or a venue that would attract all types, similar to the stilton cheese run which attracts 300 people.
Could horse power at the hall be asked to attend?
For the people that attended the day events that didn't stay over ,maybe a night ticket to see the band?
Advertising the event will be key, Facebook, all members can like it and spread the word, magazines and direct contact with other clubs.