Do bear in mind that your miles last for 3 years without any extra being added and SAN to JNB would add more than 20k to your pot. Things can change quite dramatically in that time and the miles may well be worth holding on to.

How are you searching for domestic awards? The BA website isn't great in my experience at finding AA awards. You have to look up sAAver award space on the AA website often then ring up BA to get the flights.