Am I blind - can't see it, just the old offer
It does not explain "eligible purchase" how much and on what?
It does if you click on their T&C:
* To be eligible for the bonus Points offer, you must apply for a new NAB Qantas Rewards Card by 19 April 2015 and make an eligible purchase within 90 days of opening your account. Everyday purchases exclude transactions NAB decides are wholly or partly for gambling or gaming purchases. NAB may vary or end this offer. Points will be credited to the qualifying members account within 2 months of the purchase. Bonus Points offer not available in conjunction with any other offer or to NAB credit card customers transferring from another NAB credit card or to NAB staff under Employees Choice.
So as long as it is not for gambling or gaming, any purchase will do. By implication there is no minimum spend to qualify.
I know that once where I was chasing points in the original Everyday Amex Promo that I bought a CD that was marked as a $1.00, but it rang up as only $0.01. Luckily the cashier still put it through, and a 1000 bonus points then landed in my MR account as it was a qualifying eligible transaction probably the best $0.01 have ever spent. You might be able to replicate that here to gain 40,000 QFF points!