Was extra population from the Archipelago and the Korean Peninsula need to go somewhere? KMT warloard controlling Inner Manchuria produces coal, lumber, agriculture including soybeans and Soviet Union Outer Manchuria produced lumber and tin. Northern Sakhalin produced petroleum and some natural gas.
If Japan retains pre-1931 territories, novel technology allows off-shore natural gas exploitation, greenhouse agriculture on the warmer part of Sakhalin, minerals from the Kurils, and fishing and agriculture from Micronesia. The jewels of these places: Taiwan and Korean Peninsula were either part of or per se independent countries. Japan may need to return them.
Taking the anaolgy from the economy of Hokkaido, the combined economies of Micronesian islands (Ms) southern Sakhalin (sS) and Kurils (Ks) are likely to provide natural gas (sS), paper milling (sS), beer brewing (sS), energy and chemicals from paper and brewery biomass, natural gas (sS), minerals (sS Ks), fishing (sS, Ks,), some agriculture (sS, Ms), ecotourism (sS, Ks, Ms). In other words, Japan would have
two Hokkaidos than one. Would that make a difference?
The Japanese Empire may not necessarily have an economy larger than it does now, since post-war trade within the Western world order was what made them rich. Much would depend on who the other world powers are and alliance politics, but surely more powerful than Japan in this timeline.