Gareth,
when considering 'other area' please keep in mind it may include Ermelo, Middelburg (cape or mpumalanga), putsonderwater, de doorns, pofadder, cape town and rietfontein.

if there are more boys climbing in the south, then maybe thats a good place... like alberton? Such a gym may also get attention from the vaal triangle / meyerton area if marketed correctly, i guess.
or maybe im just having more brainfarts.
depending on your knowledge of the game, I also recommend you go chat with the current wall owners. from what i understand this is a game you currently get into for the passion and not for the money.
lastly, my view is that visibility and positive attitude on the long term is what will make a new gym a success. if you are not ready to spend a large portion of your life in the gym then maybe it is not a good idea.
what I would like to see is that the sport grows (in a responsible manner) and that more areas of south africa get exposed.
good luck!