That cap of 750k points is for the bonus points (flights, restaurants, etc), there is no cap on total points. The cap for bonus points on Plat is 300k. It's that difference that has me leaning towards getting the card as I would pick up the extra bonus points without changing my spending patterns, so 450k points for $3,800 plus a few nice side benefits including an upgraded insurance plan, etc. I had looked at the benefits previously and didn't see the point in changing from Plat as most of the benefits are the same or similar but I think it's worth it just on the point difference for me.
My understanding is that the joining fee is waived regularly and I would not entertain paying that with a $5,000 annual fee. Waiving the joining fee rather than the 1st annual is more realistic I think.
If the ATO spend attracted 1:1 I'd be a very happy boy as well. I'd be flying RTW in F just for fun every few months!!!