No amount of gold 'makes' a tank if the existing manufacturing capacity is fully utilized. You can 'buy' resources (iron from Sweden) and there will be an economic benefit from looted gold. BUT the damage to the economy CAUSED by the looting and general mistreatment exceeded the value of what was looted. A (non repressed) cooperative population would have generated economic output VASTLY exceeding anything which could have been looted. in the game a 'harsh' policy generates more 'loot' and a few essentially ineffective partisans (ineffective in the game). The underlying logic for this is IMO flawed as well a harsh policy is LESS effective in generating production from a occupied nation. Slave labor is about as inefficient a system as exists. No small wonder the Germans had one of the LEAST productive economies of any major power during the war.
A series of related points I have been making all along.
German industry was fully committed in 1939 ... there really wasn't a whole lot of slack in the system. They could fiddle around the edges by, say, forex, working expensive capital equipment two shifts a day rather than one (but, as I understand it, working it three shifts a day is counterproductive for several reasons), but that simply runs head on into the resource limitations the Germans faced ... you can't produce fighters with pigs, you need, amongst other things, aluminium, and what the Germans had was already fully committed ... even the allies had issues there (Mosquitos anyone?) ...
The only real way for the Germans to expand things is, as you indicated, steal factories and resources ... other than pigs, of course , from their neighbours.
The Nazi war economy was, basically, a giant looting operation, and, when the loot had been squeezed completely out of the conquered countries, their economy started to go down the gurgler at an every increasing speed, Speer's massaged figures notwithstanding.
See Tooze, "Wages of Destruction" for the details of the situation the Germans faced and how they (failed) to deal with it/solve it.
Looting pigs, cows, and horses really only released manpower from the largely unmechanised German agricultural sector to serve in the armed forces ... in fact, the Germans did their sums in 1939 ... if they mobilised to invade Poland, they would massively reduce their own harvest for 1939, creating a famine in Germany ... unless they stripped the food out of Poland, which is why the death rate in Poland 1939-44 was so high, "Final Solution" notwithstanding.
Further, the initial planning for Barbarossa was to *starve to death* 60% of the Russian population in the planned conquered territories over the next decade ... starting by simply surrounding large urban areas during the advance and preventing ingress/egress to starve the inhabitants to death.
Only military reality intervened ... cities have other uses, as the German military realised even if the Nazi Party planners didn't.
With "economic planning" of this sort the basis for the Nazi Economy, well, it's no real wonder it lost ... decisively.
Author, Space Opera (FGU); RBB #1 (FASA); Road to Armageddon; Farm, Forge and Steam; Orbis Mundi; Displaced (PGD)