The miles junkie in me has to respond to this.
Flybuys/non-airline loyalty programs are shithouse. Absolutely, agreed 100%.
So the 1% instant cash-back schemes are pretty good. I mean its money instantly, for nothing, so can't complain there given that you were going to have to spend it anyway.
PoP - Amex is accepted at loads of places, and most places eat the surcharge, I've found.
Assuming you don't pay extra for the use of the amex - and you get the value of the annual fee back - you're generating miles for nothing, and can spend them quite easily. I don't see the issue.
That MEL-LHR F ticket is 100,000 miles and maybe ~$300 in taxes. RRP of ~$5k. In that case, it's a 5% return for doing nothing different.
So what's a good program for someone to sign up for?