I don't think your experience driving around Africa gave you a enough information to adequately support your conclusion (which I could not leave unchallenged). I mean this in a non-disparaging way: you got breadth, but not depth. I, an African, on the other hand, have depth, but not breadth.
I have some experience with both sides of the NGO coin: I've seen communities and individuals positively. From disease eradication in whole communities to people regaining their vision. People giving money are helping in most of the cases. On the other side of the coin - I agree that NGOs have a lot of fat they could cut in terms of expenditures that do not directly go to their mission, but this depends entirely on which NGO it is and what their culture is, not all of them are the same. This is an industry ripe for disruption by leaner setups, too bad VCs aren't really geared for this.
Donors are helping, but maybe not as much as they think they are (per dollar). It would be great if they would research the org they are donating to to find how many cents per dollar are going to the cause. More transparency in this area is needed.