if you give someone a pile of money and tell them to improve the world what's going to happen? there isn't a single, good, clear, correct plan of action, as far as i know. so even if this hypothetical person with a pile of money was an objective, honest, smart person, they'd be pretty unsure about what to do. and most people aren't objective, honest and smart.
so what's going to happen? they're going to push right ahead with whatever they think is right. and because they have a pile of money they have a pile of power. so you end up with this powerful person telling everyone what to do - even though it's probably not the best solution.
so it seems to me that it might be a good idea to look at alternatives. maybe your question is assuming the wrong thing somehow.
but what alternatives are there?
here's one, off the top of my head. instead of having a system where we go like crazy to make a pile of money so that we can then "do good" with it, why don't we ease off and not make so much in the first place? if we didn't try so hard to make the place unequal, perhaps we wouldn't need to spend so much on fixing the inequality.
[there's an obvious answer to that about life not being zero-sum, and i agree there's some kind of balance necessary, but i am not at all sure that we've found the best equilibrium where we are.]
here's another: give everyone a dollar. or a pig. or a chicken. or a saw. exactly what isn't so important. what's important with this idea is that you spread the money around to everyone. you spread it really thin and then let the people "on the ground" decide what to do.