This is a little complex. I’ll try to communicate as clearly as I can but please get back to us if I’m not making myself as clear as I should be:
You don’t explicitly say this, but my guess is that you have an American Express Platinum charge card? That card earns 2.25 AmEx Ascent Premium Membership Rewards points per $ spent, and the Point Hacks article you link to values those points at 1.2 cents each.
AmEx Ascent Premium points convert to Singapore Airlines KrisFlyer “miles” (ie. points) at a 2:1 conversion ratio. So for every dollar spent you get 1.125 KrisFlyer points.
If my assumption that you have an AmEx Platinum card is correct, read on…
In the example you give, you’re being charged a 3% surcharge to use your AmEx. Yes, that means that for every dollar you spend, the seller is adding 3 cents. Let’s do a hypothetical calculation:
A product costs $100. To pay by AmEx, you’ll be charged an extra 3%. Total charge: $103. That $103 will earn you 232 AmEx Membership Rewards points, which you may choose to convert to 116 KrisFlyer miles.
In effect, you’re being charged $3 for the privilege of earning points on your purchase. So your 232 AmEx points are costing you $3, which works out at 1.29 cents per point.
If you were after KrisFlyer miles, your $3 would earn you 116 KrisFlyer miles at a cost of 2.58 cents per point.
So… is the $3 worth it? It depends on your circumstances.
If you want the points simply for the sake of having the points, the answer is no, it’s not worth it. The points cost too much (ie. they cost more than what they’re worth).
If, however, you have a specific redemption in mind (say, a business-class flight on Singapore Airlines on a particular date and there’s availability on that date) and you need lots of points quickly so you can grab the flight you want, my “take” is that because these points cost only slightly more than they’re worth, it might be worth paying the 3% surcharge.
I hope that helps, but please let us know if I’m not making myself clear or I haven’t understood your question.