I know that there are new illuminated signs on the A11/M11 (south and north), in fact they've been there for a while now - all of them have large yellow signs "sign not in use yet". If someone plugged them in at least they could be used to advise traffic of the circumstances.
Equally I think that the IWM could easily afford to finance similar types of illuminated signs on the A505 and similar heavily used approach routes.
I don't know the area well enough to suggest that temporary one way road systems should be implemented for the really big events at Duxford, but whatever happens the IWM have ultimate responsible for getting this sorted, not the local councils or council tax payers.