If it happens normally then its moot, otherwise the $310p/a is smaller hit than trying to go out of your way to spend 50k in 6 months to get a 50% discount.

All the Plat cards have the standard APD advance, travel insurance, which for me is enough to justify the per annum
If you're flying enough and hitting elite or getting close to elite, you're probably already maxing out the amount of credit-card earned SPs eligble for qualifying (from the SP bonus) so really it's up to you to workout if you want to pay for another plat card for "a better" APD earn.

tldr:
get an AMEX card for "best" APD earn rate, might have limits on its uses where AMEX isnt accepted
ANZ Plat for SP bonus
and if you want to buy/top-up APD, get the Kiwibank low free visa as a tertiary card