This is for 1941
Take the infantry from Manchuria and attack Suiyuan.
Take the infantry from Kiangsu and attack either Fukien or Hupeh.
Use the transport in the Japanese sea zone to invade Kwangtung with an infantry and a tank.
The fighter from Japan can be used in Suiyuan, Fukien, or Kwangtung.
Take the infantry from French Indochina and attack Yunnan.
The fighters from Formosa and Manchuria go to Yunnan and land in French Indochina.
The most important of these battles is Yunnan as China’s only offensive piece is there. Taking Yunnan is not important. Killing the Chinese fighter on round 1 is of the highest priority and if it takes loosing the Japanese fighters to do so, do it.
The above battles are the safest approach to China on round 1. This leaves China with the ability to produce 2 infantry.Depending on the results of these battles and any reinforcements from Russia China can easily be unable to produce any infantry after Japan’s second round.
1942 is similar, and again the destruction of the Chinese fighter is of the utmost importance. Japanese fighters can be replaced. When the Chinese fighter is gone, that is it. This leaves China without any offensive pieces and merely infantry that can attack at one.
I am also not sure where you think Japanese resources would be of better use. All the Chinese territories equal 12 IPCs that are very hard for the Allies to liberate. Normally the only nation that can liberate Chinese territories is Russia and this is drawing Russian units away from the fight with Germany.
See this thread for a more detailed discussion of Japan in the 1941 Scenario.
http://www.axisandallies.org/forums/index.php?topic=13244.0