The issue with targeting ANZAC is, for me, an economic one. For Japan to acquire ANZAC’s 10 IPC/turn, they have to capture a total of seven territories. On the other hand, just four territories - Sumatra, Java, Borneo and Celebes - will net 20 IPC/turn for Japan. My alternative to your scenario is this:
J1 Move one transport and one sub from Japan to the Carolines.
J2 Declare war, then use transport + 1 INF from Carolines to take New Guinea. Also take Malaya as soon as possible (these actions deny ANZAC National Objectives, costing them 10 IPC/turn). Use naval forces in Carolines to take out ANZAC fleet.
On subsequent turns, park subs in sea zones 54, 62 and 63. This can reduce ANZAC income to as little as 3 IPC/turn, virtually taking them out of the fight without investing a significant chunk of the Japanese navy, as well as ground forces.
Well taking it also helps secure the other money islands as you got a factory there. And with just 1 country you make it a 17ipc swing. -10 allies +7 for japan. Those transports can take java the turn after.
US has to invest to get it back, its not just easy capture for them and your fleet can position off queensland and threathen haway and also india.