There’s plenty of other more valuable things that are prototyped using 3D printers, such as high end commercial machines, or components that go into those machines.
I suspect that getting hold of STLs from US defence manufacturers would be extremely valuable. Why bother trying to capture a copy of your enemies technology, when they’ll happy just send you all the prototype STLs. Even if it’s not defence, don’t you think access to prototype components from EUV machines from ASML would be crazy valuable to Chinese companies trying to close the gap between Chinese and Western chip fabrication technologies?