You'd be in a better position to do just that in a place that costs less standard of living wise. Don't forget that earning a fat whack makes it a lot easier to go backwards than forwards too. I prefer to live somewhere with less stress period.
I agree that if the cost of living is higher and your income doesn't grow to match, it's a problem (i.e., don't stay in the poshest suburb of Jhb if you're going to Jhb to increase your income). However, most of the time, you can find a comfortable area in the new city which has a similar standard of living (but higher cost of living), that scales with your income.
My personal situation nearly 15 years ago was that I went to Silicon Valley, and within a few years was earning around $200k/y. Sounds awesome, but over there, it put me firmly in middle-class bracket. My life style was basically, driving a Honda Accord (which I had for 8 years), while living in a fairly basic 2 bed/2 bath rental flat (me, wife, dogs), saving for a deposit for my own flat, paying the bond on my house in SA (which was tiny by comparison to everything else), eating out twice a week, flying economy in off season to SA or England every two years or so to visit family and friends. Really, nothing all that extravagant. Still, I had enough saved to quickly pay off my SA house completely, and by the time I was a few years into my own apartment (mid thirties), my net worth was large enough that if I wanted to, I could sell up (or rent out), move back to Cape Town and retire.
Although comparing SA to one of the most expensive areas in the US makes the point in the extreme case, a similar dynamic exists in SA (and anywhere). Most middle class Jhb'ers can retire in East London wealthy or Cape Town if they wanted to, most middle class East Londoners can't retire in either of these places.