Well, actually, Nigeria is one of the wealthiest countries in Africa due to huge oil resources. It's GDP is above that of countries such as Israel, Egypt, and even Pakistan, and is rising. It's the eight most poulous country in the world, as in, roughly as populated as the US East coast (150 million people livign in an area of the same size).
http://en.wikipedia.org/wiki/Nigeria#Economy
While human development is rather low, I guess the middle class is large enough to justify a park. Remember, Lagos is larger than New York in terms of population, and even though the income rater are quite much lower down there, and half the population is less than fifteen years old, there should be at least a five-digit number of people who can afford parkgoing.
Also, remember that Nigeria is a growing economy. It's GDP growth is around 28%, which means that if it keeps growing like that, it will almost have tripled by the time the park opens. I'd say that it will be a wise move by Six Flags to be established there when the boom hits. Though, we will see red numbers the first few years or so.
Also, they get a place to put Astroworld's SLC.
