I think there is no need to maintanance, because you dont fly training missions with this airkrafts. You simlpy make them flyable, add your gudgets and conservate them.
Aircraft being put into storage need maintenance. If it is short term, airplanes have to be run up and taxied once a month to ensure everything is in working order. This is done to ensure no water has gotten into the engine fluids, and if any did, they would evaporate due to the high temperatures. With long term storage, this requires the draining of fluids, possibly replacing lubricants with a fluid that is designed to prevent internal corrosion and drying out of the seals (pickling), plugging up all areas where birds or bugs could nest, installing dehumidifiers in the engines and in the airframe to prevent corrosion and to prevent water from getting into the engine, and the periodic checks on humidity. When you are pulling aircraft out of long term storage, you have to drain the preservation fluids, replace with the appropriate fluids, check engines and perform a multitude of tests to ensure all systems are operational.
No, the only use for these old birds is as a target drone or for scrap metal. Maybe the airplanes that are in extremely good shape can be sold as warbirds, but that's about it.