At this point in the war, I think it is best to view every allied aggressive action as an opportunity to engage allied forces to your advantage. Time is slipping away, as is your advantage in land, naval, and air power. The allies will achieve parity with you in 4 or 5 more months and surpass you in 8 or 9 months. His move into the Marshalls is premature. He has neither the naval air nor surface capabilities to support these positions at this point. If he tries to continue the offensive there, you will have additional opportunities to sink allied CVs and surface assets, as well as kill good allied pilots. In my opinion, get after him there. At the very least, if you move into the Marshalls in force, you will have the opportunity to destroy his expeditionary forces on the ground there.
Are the CVs really necessary to support the Australian campaign at this point? Certainly to provide cover to your major transport groups as you pull out, but now? Could the CVEs and slow CVs (i.e. Junyo) serve your purposes in Australia, freeing up the others to seek a CV battle in the Marshalls?
As an aside, in my opinion CentPac is the most vulnerable and therefore strategically important position for Japan. It is the quickest route to the home islands. CentPac must be defended tenaciously, in my opinion.