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Well, it is easy to wipe off $30 from any annual fee with the Small Business Saturday benefits, so that does lower the threshold of having a PRG in addition to a Platinum.
If you can make great use of the special offers, then do that, but it might be better to get a lot of low-priced Green than Golds and PRGs. Most of the offers I get on PRG and BCE are $10 off $50 or more for stuff I don't really need. If I was getting $10 off $10 or more on something every week, then it would make sense to have a lot of cards. Maybe you get better special offers than I do.
For me, though, it would also mean having a lot of junk I don't want. $10 off $10 or more at Costco would be good, but the merchants tend to be less useful.
Small Business Saturday = $30 x 1 + the number of AU cards you have.
I never buy anything I wasn't going to buy in the first place. My use of the offers falls into two categories: saving on existing spend (e.g. groceries, a good example is the current Walmart offer which I'm letting my parents use), or buying easily liquidatable items (e.g. cash equivalents like Visa gift cards). An example of the latter are the recent Staples and Best Buy offers, both of which sell Visa gift cards. Or the Sony offer which lets you get a PS4 for $260, which can be resold for at least a $50 profit on eBay (after deducting eBay and PayPal fees).
I'm surprised Amex isn't able to detect (or doesn't object to) your purchase of gift cards as part of offers. I thought more and more retailers were requiring gift cards to be purchased with cash - or attaching big activation fees.
I've not tried to pursue any manufactured spending, but I do see how you can make money at it, even taking the risk of being shut down.