You will probably know by now that Sygic don't do SA either.
When I was visiting there I found that Tom Tom 6 on my WM phone (HTC Touch Diamond) with their SA maps was very good - got me to all the places I needed and address accuracy was also good. However TT have not yet released their Android version of their software (if they ever will).
You could try emailing Sygic to see if they have any plans to release SA maps - I know they are launching a new version of software and newer maps soon so they may be. Their support is very good. Or wait and see if TT produce an android version, but don't bother contacting them to ask because their support is awful. Or wait until HTC bring out the Android 2.1 version for the hero, which should have Google sat nav on. But that requires downloading the maps over the phone so not sure how good or expensive that would be for you - how extensive is the 3G network now?