It could make things worse. The general standard of politicians in Africa is terrible. It wouldn't be fair for black people worldwide to be judged because of African leaders like Zuma, or Mugabe. Too an extent this already happens, ask a Nigerian how they feel about constantly being associated with fraud and scamming.
Someone mentioned Israel earlier - I think that there is undoubtedly more antisemitism worldwide because Israel exists. A lot of modern antisemitism comes from the Arab/Israel beef. Jews were reasonably well integrated in the Arab world before the establishment of Israel, nowadays there is a lot of antisemitic sentiment within the Arab community (and within the Muslim communities in Europe). Similarly there is anti-antisemitism on the left, which all stems from people judging all Jews for Israels actions.
Similarly a corrupt/ badly run African state reaching the status of a global power, could unfairly tarnish how people perceive people of African descent.
Therefore to be of benefit - rather than just being a "power" it would need to be a "good" state, that is respected for how it is run, and the values it promotes.