Been there, done that, rather not have to go down that route again.
Did five events for charity in six years (three cycling, two others) and each time I raised less and less money than the time before, despite trying harder and harder to do so - in fact on my last attempt I probably spent more time trying to fundraise and chase up promised donations than I did training for the actual event! I think people were just getting charity fatigue, plus as my circle of contacts was never that large to begin with, I was essentially having to tap up the same set of people each time. But I did get two very nice cycling jerseys out of it all which I still use today (one Mind, one Macmillan - one other charity only offered me a t-shirt!)