Yeah, the whole point of the advice to "win the Battle of New Caledonia" is the possibility of achieving a meaningful victory over the Allies on favorable odds, thus postponing the Allied juggernaut. If he loses, of course it's bad news. But in July '42 shouldn't the Japanese seize a chance to thrash the Allies under favorable conditions? Chances generally don't improve as the game goes on. If not now, when?
I fully agree. Now or never. It will be 9-12 month before the Allied CV force will again be a serious threat (i.e. what about the British flattops in your game...?), and until then I would seek opportunities. And this one seems present, and it has strong strategic implications.
It will force your opponent to commit his navy and air force, or loose very valuable assets, some of the few he has at this stage to himself stage something more than a raid of minor impact. You have the initiative here, and with KB you can keep it -- which raises chances that he could make mistakes. You can make this the battlefield of your own choosing, and have him fight at your odds. Looking at Efate and what parts of the map you show, and considering that he lacks CV support, it doesn't look like this would any longer be the spot of his choosing, where he'd place more units now. Depending on the next 4 weeks and his supply situation, I wouldn't even be surprised if you'd note him sneaking out elements.
Chickenboy certainly has good points there, and maybe the probability to survive longer for the Empire increase somewhat if you'd cut the losses now and leave "Dunkirk style", but I would always agree with those that advocate more aggressive, bolder stances. Just makes for a more interesting game I find, and it would be more in line with my typical thinking. It's the initiative you'd surrender with that now, and offer a psychological victory, both if which I believe you don't yet have to give away that cheap from what you explained. It seems to early to turtle. This whole affair can be turned into much more than a purely tactic battle with little to now implications elsewhere -- it depends on your opponents reaction. Noumea with its large airfields and port is key to the Coral and Solomon seas, and a good threat to the LOC into the Australian EC ports, and a thorn in the side for any major offensive through this region.