Staying OT regarding the main topic, and sticking with Gift Aid...
There was an interesting bit on "Simon Evans Goes To Market" on Radio 4 recently, where someone explained the consequences of Gift Aid as part of the bigger picture. Basically, when you tick the Gift Aid box, the government pays some more money (out of your taxes) towards that charity. But that has to come from somewhere - basically it comes from where your tax money would have gone to, like the NHS, education, policing, etc.
The pundit was saying that when you consider ticking that Gift Aid box, are you really saying that you care more about Ely Cathedral than you do about healthcare?
I'd always just assumed that ticking that box was a Good Thing to do, but this did make me stop and think.