As for the Kenyan option:
Unless you want to be a full 100% tourist who will stay in a nice hotel, I do not recommend staying in Nairobi, I mean you can stay up to like 23rd Dec.... Then you should move other destinations like Nakuru etc
Nairobi usually gets abit lonely just before 25th till after 31st. A majority of the people go to their village homes, Ofcourse this is good from a tourist's perspective since there will be no traffic jams, but given that you are African, you might not have a nice experience without Nairobians filling up the place not unless you know exactly which places to find them(those who remain).
Since I don't know what you are looking for in your holiday, i wouldn't know what alternative to recommend you... I can however tell you that thousands of Kenyans flock to Mombasa during that month. Even media stations shift their broadcasting location to mombasa, the president also conducts his business from the Mombasa state lodge. Last year there was a record number of vehicles with Tanzanian registered plates... You couldn't spend 5 minutes without noticing a Tz plate number. So you will get plenty people you can associate with.
The next destination I will recomend is Nakuru... You have a number of wildlife, lakes, waterfalls, Mountains and a nice nightlife for entertainment all at you disposal and its also very urban just like any EA city so you wont feel like you are in a remote location