I've been going to airshows of all sorts for nearly 30 years man and boy and in recent times I've gone both as an enthusiast and as a parent.
Personally, I think there is a lot of variety in UK airshows but from an enthusiast's point of view perhaps certain locations tend to conjure up particular expectations.
Think of RIAT and one tends to think of long queues, lost of fast jets & heavy metal and long lines of static aircraft. Old Warden tends to conjure up thoughts of props, vintage aircraft and aerobatics. With Farnborough it is new designs, generally quite staid displays and perhaps not so much excitement as there used to be about the place. Think 'Duxford' and one tends to think of WW2 vintage machines doing choreographed recreations of various events.
The truth is that most of these locations do offer quite a lot of variety but perhaps two points are worth raising. In the first instance I have to confess that as the years go on my ability to be truly impressed by airshows has slowly diminished. I think this is partly because while, for example, strawberries and cream might appear wonderful on your first experience, its appeal is much less after the umpteenth time and perhaps we enthusiasts in the UK have become a little spoilt? The second reason is because perhaps some events have neither the capability nor the desire to offer total variety and so they have concentrated more on certain aspects; this can make such events much more predictable in terms of what a visitor can expect but I wonder if this gives them so much appeal for the family?
I took my son, his two friends and their father to RIAT this year and it was the father's view which surprised me most. Some said that RIAT 2004 was a little bland but he (who hadn't been to an airshow before) was truly impressed ... I have the bottle of Bells he gave me to prove it! [... and a request to do the same in 2005.] Actually even RIAT has its variety (the 'lazy lunch') but perhaps its sheer size (and cost) is a factor against it.
For me as the enthusiast without doubt it is the unusual or the unexpected that appeals. That means that the Italian G.222 display at RIAT will always make me stop and stare, as would the French guy with the geese or even the South African 747. I also have fond memories of a superb display at Middle Wallop some years ago by a guy with a Piper Cub so I still think that an airshow offering variety appeals.
For my son and his friends fast jets are impressive just as much as an Su-26 display. I suspect that RIAT was actually too much in some respects - perhaps an airshow works best if it is a filling meal, rather than a gorging feast?
... and the conclusion from my ramblings? I think more variety is needed for all concerned. 'Themed' displays are OK but they do tend to get a bit boring for some people and a work colleague (not an enthusiast) said just that about a recent Duxford show. I also think that smaller events probably do work better - fewer queues, lower prices, less crowds ... but then again I shall always enjoy RIAT!