I'm not sure if the format of the Plassey would work any more; it was pretty basic by todays standards and there was little room to expand.
A really good vintage rally in the Wrexham area would have a place in my diary.

I can not think of any good locations in the Wrexham area though.
the place just this side of high town, where the car boots are is probably too small, and too close to town.
Bangor on dee, race course has potential.

Eaton Hall would be another good venu, there is a dissused runway there loads of hard standing. Though that has not been used for events for a few years.