I agree that I should have looked around on flyertalk prior to my trip, so that I could psychologically prepare myself better for connecting at LOS.

I did do my minimum homework - I did check the Nigerian Embassy online prior to my travels and got a visa for Nigeria before I left the US. But even that was a hassle - one has to pay a fee to the Nigerian Immigration Service online, and then make a payment to the Nigerian Embassy in DC separately.
I wonder what would have happened if I had showed up for transit in Nigeria without having a visa in my passport! When I checked in with SA at MPM (for my flights to JNB and LOS), the airport agent did not bother to check if I had a Nigerian visa. I suppose I probably could have bribed my way thru the immigration service at LOS - but at what price?!?

I did think about the possibility of finding seats on the JNB-ACC flight and then connecting onto UA at ACC, but knowing that the CO BF product is better than the UA biz product, I decided to just give the LOS-IAH flight a chance. At least that flight did turn out to be a very comfortable one, since the BF cabin was only 1/4 filled!