I agree with most of your comments Greg but I reckon Northern Ireland could hold such an event itself.
Not wishing to ignore our friends in the South,but I think the South does OK for airshows in it`s own right. 
It`s a fact that the RAF definitely don`t send enough different types to smaller airshows;their are plenty to the big UK shows such as RIAT,Wadddington,Duxford,Leuchars etc.
The RAF have a list of priority shows and they send all the good stuff to them. 
 
 This year there isn't meant to be displays from either the Harrier,Chinook or Tornado's,but they role them out for the big shows.
The simple fact is unfortunately that the smaller airshows don`t get the opportunity to book some of the more interesting aircraft. 
I always thought Newtownards was a good venue,the only slight drawback was the runway length.I know they have had airshows at Aldergrove in the past but I was never at one and I don`t think they would be too keen.
Aldergrove along with most UK airports have become security obsessed of late and I can`t see an airshow happening at any major UK airport anymore.
St.Angelo isn`t ideal either as the runway sits in a "V" shaped valley and the high ground on two sides make jet pilots VERY nervous. 
Last year on the Sunday of the Portrush airshow the weather looked pretty awful over Portrush and we took a drive to Beone beach.
I think it would be a better venue than Portrush as the beach is very long and has a natural display line.