Make the exX cubemaps much less intense. Basically, I will cut a deal: The more rusty...

Make the exX cubemaps much less intense. Basically, I will cut a deal: The more rusty and dark / solid a metal texture is, the less it will reflect (barely visible reflections). However, the brighter and more polished a surface is, the more mirror-like it will be. This should be quite fair and not exaggerate the effect, since most textures are rusty or non-polished metal plates.