My view of national events include anything that is at a large venue with plenty of public footfall, and lots of club cars (ie huge from the PR front)

NEC Classic show
Stoneleigh restoration show
JAE
Silverstone Classics
(Le Mans)
(Any Santa Pod stuff maybe....)

Tatton & bromley have traditionally been organised by local areas, and despite being large events, still fall in the area events.
This is what all areas should be trying to achieve: a big event/show in thier area IMO.