Your post on this is quite valid moving to Krisflyer is much better - singapore airasia and also asiana airlines. But it becomes a cost issue now with annual fees and maintaining my NAB Card.
Any cards you recommend for Krisflyer with low annual fees - this is subjective.
Well looking at the cards you mentioned at the start:
1. NAB Platinum Amex (will not use visa as poor return on 0.5QFF/$) - I work at nab so no fees. 1.5QFF/$
Clearly you're stuck with either QF or VA direct earn cards if you want to take advantage of the free NAB card. IMHO though, you shouldn't feel like you have to use one of the NAB cards, just because it's free. I have free cards that I never use.
2. David Jones Amex - 2.25QFF/$ for supermarkets and petrol
You can get the same card but sign up to Amex Membership Rewards (MR) instead. That allows transfer to 8 different FF programs, including SQ. The MR earn rate is also higher (1 reward point = 1 MR point = 1 KrisFlyer point, compared to 1 reward point = 0.75 QF points). Another option (which I use) is the Amex platinum edge. $195 per year, but you get a free VA domestic flight each year (easily worth more than the annual fee), and it earns 3 pts per $ in supermarkets and 2 pts per $ in petrol stations.
3. Citibank Signature Qantas (conditionally approved) will get bonus of 80k, waive annual then close or try to switch over the free fee for life.
Again, you can choose to earn Citibank Reward points instead of QF, and they transfer to KF points (or Velocity) at a rate of 1.5:1.
The other great one for KF and other programs is Westpac Altitude Black. This is more expensive ($395 per year), but worth it if you're going to spend a fair bit.