When redeeming my 93,000 Westpac Altitude Rewards Points, I noticed it was cheaper to redeem 4x $25 gift cards (21,000 points) instead of 1x $100 card (23,500 points) for AmpolCash.
Using this I managed to redeem 17x $25 gift cards, and used the remaining points in exchange for ~$15 'pay with points' (bought some Amazon gift cards on shopback).
Total value redeemed $440.
You have to be logged in to see the price, but I have an image here that shows what's going on.
I assume you're referring to this card bonus https://www.rwrds.com.au/credit-cards/westpac-altitude-rewar…
In which case why wouldn't you go for the annual fee rebate instead? It nets you more at $450+3000 leftover points and is essentially real cash.