To be cynical for a while:
It's actually quite possible this is a net benefit to the country. The money coming in obviously "drips down". Officials maybe also take bribes, I don't know.
It may even raise the profile of Nigeria for aid - "look how desperate Nigerians are to stoop so low, if we address poverty there then it will also address this problem" (squeaky wheel gets the most oil, etc.).
Of course 419 refers to the article of Nigerian law that prohibits such actions.
See the Excel sheet here:
http://www.doingbusiness.org/documents/Simulator_2010.xls
Nigeria is ranked 125th in the world for ease of doing business.
One of the requirements for a good business environment is stable, largely non-corrupt government, which is obviously lacking in Nigeria.