I don't want to sound rude, but I really think you should reconsider that statement.
The Western African civilizations, such as Mali and Songhai, were centers of Islamic learning for several centuries. That's right - they were centers of learning. Their trade was so prosperous, and they were so wealthy, that legend has it that when Mansa Musa visited Mecca and gave out some gold for free, he actually caused the market to go kaploop for a year. And note that these empires' armies were not like the stereotypical tribal warriors running at each other. They fielded large armies organized along the lines of infantry, auxiliaries, and heavy cavalry, much like other powerful states around the world.
We may also take the Berber/Moorish civilizations, for example - they were not the same as the Arabic-Persian Islamic civilization, and they played a huge role in developing Spain; for a time, Moorish-ruled Spain was the most intellectually and culturally advanced society in Europe, and it was also a surprisingly tolerant place, too.
You could also take a look at ancient Nubia. After being dominated by Egypt, they then conquered Egypt and ruled it for a century; even after so, and even though they were heavily influenced by Egypt, they developed their own unique culture, one that successfully resisted Greek, Roman, and Arabic invasions for centuries.
Or, perhaps, look at Ethiopia. They were one of two only African nations to not be colonized by European powers.
Another example are the Swahili, who were famous traders along the East African coast. They played a pivotal role in the Indian Ocean trade for more than a millennia.
Now I do think myself that probably the vanilla game only needs one sub-saharan African civilization, but frankly, I think you really have to think twice before saying that African civilizations didn't develop their own unique, prosperous, and urbane cultures.
Good point about the african things - I'd love a few of the ones you mentioned to be included in an expansion, the Moors especially.