Completely reworked much of the master material and it has really transformed into something much better than before. Added new detail to lights and completely revamped the original metal, rust, and paint materials to have better surface properties. Things are much less busier and do not have odd height details. Overall I am very happy with these results, and I do not envision much more work being needed at this point other than some cleanup and checking each material channel to ensure that the layers are interacting/blending properly.
These are still 2048x2048 pixels in resolution. I do not think any up-resing to 4k is necessary at this point, and I am too far along to take time (probably at least a week) to re-bake the hundreds of texture maps that would be needed to undertake that task.
Above tested in a custom warm lighting condition to simulate a suitable game environment