My skepticism of IC buys goes back to Revised. It seems that the goals people think they can accomplish by buying ICs can often be better accomplished by using the ICs you already have.
If you aren’t buying the IC to maximize efficient production (as Japan needs to), then they need to deliver a strategic benefit that justify their cost.
Certainly Japan can profit from at least 1 IC. Probably 2, maybe 3.
UK…idk. They’ve got plenty of ICs. Egy/Persia/Iraq ICs can be useful in the right circumstances. But I wouldn’t be dogmatic about building them every game, considering the liability of them possibly falling into Axis hands.
USA…well if they control Norway/Finland then it makes sense to build there.
Other then those I have a hard time justifying them. I suppose there is a case for a German IC in Romania, but I’m not convinced.