Well the Trax attendance this year was 16.8K which was up 30% on last year, so I'd be very surprised if Nat Day (not taking anything away from the event)got near that.

Having said that, it's a show aimed at a very niche market, and so if you take just Ford products pretty much everyone there is your potential customer, whereas at a multi-marque show only one-in-ten will be interested.