To answer just some points, I agree about Mulhouse but the point was not a systems failure but a pilot failure using a system. Perhaps not typical.
Air shows are undoubtedly popular with many regular visitors over the years and some visiting many in one year. Adding them all up however and the numbers are minute. They are really preaching to the converted. The established shows are so few that most people don't have access. The free seaside shows are popular but I don't know how they cover costs.
An attempt to start a new show at Abingdon to attract the Londoners was an abject failure on so many levels. I think Lincolnshire has dropped off the circuit now so what Military shows remain?