Becasue of the malfeasance of Sept. 11th, I believe we should eliminate all air shows until we win the war on terrorism.
What would you consider overdone?
For demo teams such as the Blue Angels, Thunderbirds, or Golden Knights, airshows are their job. The costs are justified by the goodwill and recruiting aspects generated by the shows. That's no insignificant thing - catching young, impressionable minds and turning them on to military aviation is a good thing, even if they never wear a uniform. Training military aviators and their support teams is an expensive, complex business, and we can use all the support we can get. Both in and outside the services.
The aircraft detailed to smaller regional airshows are often there courtesy of Guardsmen or Reservists on active duty weekends. Had they not been flying there, it would have been somewhere else. Again, it seems to me that it's a good idea to show the taxpayer what his money is buying and to say thanks.
The aircraft you see at airshows along with their crews and support people are a tiny fraction of the entire inventory. If you believe that we're diverting a significant part of our forces away from vital duties to "make show", I'd suggest that you're mistaken. Ditto parades.
We have a lot of things to worry about concerning our war on terrorism, but airshows and parades aren't among them.
Air defense should be their job.