While I agree with the thinking of Johan, I have a slightly different take on your question and thus a slightly different response.

For someone who's traveled and has experience with "Africa" (and I know that term is much too broad) on a personal and/or professional basis, selecting and working with a "local" (e.g. in Africa) travel agent is a good idea. You would already know some of the general things and have some general ideas about what you want/need and are tapping into the local's experience and network to get you what you want. While I've never met Johan, based on his reply, that's exactly what he's doing.

But, in your case you don't have that experience with Africa. While you're certainly a seasoned traveler, you also know (or feel) that Africa is more daunting. I'd tend to agree that Africa can be "daunting" and certainly agree there are numerous choices and other issues associated with travel to Africa.

In your case my advice would be to go with a US-based travel agent who you comfortably feel specializes in Africa. Much like one would consult a number of professionals for specific work on one's home, I'd recommend working with a number to see what they're offering and advising, asking questions of one based on ideas/information provided by the other, etc.

Not to sound xenophobic, but you'll have the benefit of an American's perspective on the experience. Much the same way I'd want to talk to an American travel agent or even you who's experienced in say, China, about what it's like. I'd appreciate a "you know how in America, you do/don't do XXX, or would want to go to YYY or never go to YYY, well it's that way or not that way in China...." If you're working with an agent who has true experience in the region, you'll be getting that type of advice and helping you make good choices.