Apart from lack of aircraft (particularly British, we are now largely a component maker) the actual flying display has been reduced to a mere two hours and is a shadow of what it once was. I blame the increasing regulations which means the display line (and all displays now suffer in the same way) is too far removed from the public and height restrictions also contribute to a less than spectacular event. If the aircraft are not brought back in view of the spectators air show attendances will drop off further (see RIAT thread) and the shows will die. Only the hardened enthusiasts will bother but they are not sufficient to make the shows economical.
Both Farnborough and RIAT need reinvigorating to attract the public back