Grob Driver, you've been listening to far too many silly rumours from the sounds of it.
Brunty have never had plenty of money - CAA approval/BAe back-up was always the problem - though they may not have realised quite how expensive doing things properly would be. Only when Marshalls got behind it all did it look likely that they could get anywhere, and that's when fund-raising seriously began.
Americans helping for flight testing time - this was an entirely scurrilous story dreamt up by a little weasel by the name of Nigel Pierce who started up a club of sorts based around XM655 at Wellesbourne, promising it would soon be flying with American money, doing work for the USN etc. Needless to say he disappeared into the night with everybody's money. It now crops up as a rumour around 558 of course, as no juicy rumour ever dies entirely.
Money raised from air shows at Brunty... wasn't much and went on getting new exhibits and maintaining existing ones. Unfortunately the big hangar is far too valuable as a revenue source for storing things to be given up entirely to putting aircraft in - 558 costs the owner a great deal of money, taking up half the hangar as it does. As for being the next Duxford, one of the driving forces behind that idea was Nick Grace and sadly he is no longer with us - and with him died those plans.
At the end of the day there are plenty of static Vulcans, and if there is a chance of seeing 558 fly in another country, but none here... then it's an easy choice to make, particularly if you are the owner, and it's costing you wads of cash just having her sit there doing nothing.
Personally I'd think it was a bit of a kick in the teeth to those who have donated money over the last 2 years but I can see the reasoning why. I agree with you that no way should the BBMF be cut down to help fund the Vulcan... but get rid of a Red or two, fair enough. Paint the big V red white a white speed stripe and call it Red 9.