I wouldn't try to reduce the fender thickness too much. Just simulate the rolled edge on the outer edge, then blend it back. You'll want to smooth it back far enough that probing fingers won't feel any glass matt texture.
Most people will be using their eyes and fingers to check out your fender lips - few of them will have calipers, so they probably won't realize how thick the material is.
I glued 3/8" thick closed cell foam to the underside of the fenders to protect from rocks being thrown up by the tires.
regards,
Jeff