@misoverssaturated - Thanks! I will try that.
Meanwhile, some tests on the dielectric material: These are glass cylinders with the smudge texture applied only to the outer polygons of the shapes. The rest of the surfaces are clean glass.
Transmissive Blur, with values from 0 to 1:
Transmissive Blur, with values from 0 to 1, and Transparency, with values from 1 to 2:
The supercharged value in the Transparency map makes light spots on the darker surfaces of the glass, but whether they feel like specular values depends on the lighting position (note that they don't appear on the far side of the glasses) The also don't hold the detail of the fingerprints on their own, so a blur or bump remains necessary.
Transmissive Blur, with values from 0 to 1 and Transparency with values fixed at 1 to 1.25, so that accent the blur effects, but the hot spots aren't as noticeable (No Transparency texture on the 0% control glass):
I am not sure at all if these will work in the original file, since they rely on a specific circumstance: The Transmissive Blur doesn't actually reflect a white light, it is redirecting the light from the white marble tabletop. Once I put this in an environment where the HDRI and the table clutter has other colors, the smudges would "reflect"/redirect other colors than the greasy white specular value I'm trying to emulate.