Where industrial plant was concerned, I suspect that the immediate effect on the German war effort would have been minimal. In particular, much time would have passed between the discovery of undamaged (but far from operable) factories and their conversion to purposes supportive of the German war effort. For one thing, even without "scorched earth," the Soviets would have removed the most portable (and hard to replace) elements, things such as gauges and specialist personnel. For another, it would have been difficult for German technicians to adapt quickly to factories designed according to the Soviet way of doing things.
In the medium term, the Germans would have been able to adapt Soviet facilities to such tasks as vehicle repair. The German technicians involved in this work would not have been able to make full use of the Soviet facilities. Still, a field repair shop set up in an abandoned factory would have been able to perform a wider range of tasks than one located in a barn. One might also imagine clever engineers using Soviet elements to upgrade or even improvise items of equipment. (I am thinking of Major Becker, of the reformed 21st Panzer Division, who made use of an otherwise idle Hotchkiss plant in France to create a variety of home-made assault guns.)
In the long term, one can imagine a German program to exploit these facilities in a systematic way. The trick, however, would have been adjusting German industrial culture to factories that had been designed for Soviet-style mass production. This, I think, would have been extraordinarily difficult.