The single least-controversial thing you can say about foreign aid and third-world development, is that it's really, really helpful for the developing nation you're trying to help out to become less corrupt. Since the World Bank is supposed to boost third-world development, one important focus of its mission must be improving developing world governance. Thus, it's a really bad idea for the head of the World Bank to be caught ordering his subordinates to give his girlfriend a $50k / year raise and then get away with it.
I was considering writing a sentence here that began "if the Bush administration cares at all about . . . " but that's obviously a non-starter. The question is what leverage to congressional Democrats have that might help shove Wolfowitz out the door.