Personal preference on my part. Hub and spoke Civs, man. They can put their spokes in my hub any time. ;]
Well, that and the fact that iimbongi used to live as close to the palace of the chief as they could. Also, they're the single most important part of the incredibly rich Xhosa oral tradition, being, er, the people who remember all the stories that comprise the incredibly rich Xhosa oral tradition. If you want to represent Xhosa culture, this is a quick and easy way to do it without getting bogged down in the African equivalent of the Hundred Years War.
Oh, and if that implies they're not relevant to modern South Africa, keep in mind that at Nelson Mandela's presidential inauguration, he was preceded by an imbongi. So there's that, too. =]