Actually when I spoke to a South African (I know its anecdotal) he said the biggest issue for him was the sports boycott. No international rugby.
Now at a government level that probably meant nothing but the lack of access to international banking and credit was making a huge difference. They could see the west charging ahead in the 80's and 90's but the country was slowly going bankrupt.
As I said earlier I wish I had some magic bullet to fix the issue but sanctions are all I can think of that MIGHT work.
Its worth a try.