Newquay Airport is not such a 'huge site' as the former RAF St Mawgan which still operates the former camp area and a substantial parcel of land to the North.
There are several reasons for the museum being very difficult to sustain. It is a visitor attraction that has to compete with hundreds of others in a area that is unable to be sustained by the local (low) population, and has to rely on the summer trade which in reality is only 20% of the year. It is essentially an 'enthusiast' venue, which of course reduces its chance of income and has to try and promote itself in a very competitive market place. When you consider they are in the the same market as a visit to :- Lands End, St Ives, Eden Project, Flambards, National Trust locations, St Michaels Mount, Minac Theatre, plus a shed load of others, then the picture becomes clear. As to the One Eleven and VC10 Tanker, they have a dubious future unless someone decides to go down the 'food venue' route with them, (but where).