Developed industry makes looting more profitable but you've got to build industry and turn the resources into a powerful army. What is really attractive is seeing level three and up army production facilities early in the game when you are only building level one or two armies. If I can take over a country with high level facilities then I don't have to waste resources building my own and have an added bonus of front line production.
So other then army producing buildings, build away. I never seem to have much surplus. Pedal to the metal building armies. And having a level 5 tank plant when you only have level two tanks is a waste of resources. It doesn't build them any faster. You could of had allot more tanks instead.
