Assuming you're only after the points earn you can get the same earn-rate and lack-of-points-cap from a WOW QF EDR card, or a better earn rate (1.25 QFF points per $1) but with a $200,000/year points cap from a Citibank CitiBusiness Gold - and both have a far cheaper annual fee ($99 and $149 respectively, vs $400, IIRC).
If you were interested in getting an unlimited Priority Pass anyway the Investec Signature Card isn't too bad, given the unlimited Priority Pass goes for US$399 by itself (even with discount it's usually still over US$300). The Platinum Card doesn't look particuarly exciting though unless I'm missing something.
As a current Investec customer (home loan) I got this offer too - but for the high annual fee, the poor sign on bonus and the points earn it's not even worth a look. I'm sticking with Citi Selct and Citibusiness Gold after the Amex goes post 1 October.
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