I've been having this debate with myself for a while now and after doing as much research as I can stomach my final conclusion was that it depends on your view of what is going to happen to the country.
Yes, Pension/RA, do provide some tax benefit in the short term and gives you a bit more disposable income while still saving. You will eventually be paying those taxes at a lower rate on a higher amount. So its effectively a zero-sum game.
If you are very optimistic you could try to max out your R350k/27.5% allowance, toss in a TFSA and then take whatever you have spare offshore. You've thus covered your tax benefit and diversified somewhat.
A balanced view would possibly do 50/50 local and offshore, missing a portion of the tax benefit unless you really have a lot of surplus cash around.
Pessimistically though, taking into account everything that is going wrong, and if you read the likes of Johnson and Roodt you wouldn't be touching any local RA's/Pensions irrespective of the tax benefit. That's not to say you shouldn't be saving! Just don't have your money in SA, rather focus on converting what you have to USD and investing offshore as far as possible. The likes of EWC, NHI and prescribed assets along with the ANC's inability to take the hard decision's the country actually needs is not providing much comfort in the long term. If things do come right you could always bring your funds back and invest locally again and in the alternative you have reasonably liquid cash should you need to leave at short notice.