Last time we had a major change in 2015.
Westpac bumps BNZ as Air NZ points partner
BNZ sent email out. Subject Line " Don't let an airline dictate your bank".
It’s effortless to be better off at BNZ.
After 16 glorious years, we’re retiring the GlobalPlus fleet, and bringing them in to land. From 1 May 2015 you'll be enjoying a boosted cash back earn rate on your BNZ credit card*. This is just the start of the many new rewards you'll get by being with BNZ. You'll be receiving a letter with the details of all your benefits shortly. We appreciate you being with us on this exciting journey to great new rewards.
A great new generation of rewards are coming. 
Since the ‘90s, GlobalPlus has taken New Zealanders to amazing places; we’ve enjoyed the excitement of earning points and redeeming travel rewards.
Times have changed. Few people want to be tied to one airline, or to one type of reward. They hate it when points expire, or when the flight they want is one they can’t get. The choice was plain and simple at BNZ: to put you first. With cash the choice is yours – cash to fly, cash to buy or cash to save.
Keep using your GlobalPlus card as usual and you’ll keep earning Airpoints™ until cash kicks in on 1 May 2015.
Westpac sent email out. Subject Line: "WLG Base, you're ready for take off with a new Westpac Airpoints Platinum MasterCard"
It's great to have you on board with the new Westpac Airpoints™ Platinum MasterCard®. We'd like to say a big thank you for choosing Westpac – we're looking forward to helping you get to your next destination faster than ever.
As you know, your card offers a range of exciting benefits and we've recapped the very best of them below.
Turn everyday spending into an adventure
Your new Westpac Airpoints™ Platinum MasterCard® opens up a world of great benefits that kick off from 1 May 2015 – you'll earn 1 Airpoints Dollar for every $75 you spend on your Airpoints card*, plus 3 x Airpoints Dollars from 1 May until 31 July 2015. We're even waiving your annual credit card account fee of $145 for the first year.
Your new card will arrive towards the end of April, with Airpoints earning from 1 May 2015.
At the time there were a number of incentives to change. I finally switched when I was offered an upgrade to Elite.