The dust covers, rear damping is there for a reason. Peter Walker knew what he was doing and I am guessing the man probably forgot more about electrostatic design, theory that most people will ever know.
The rear damping is to control panel resonances. Remove it you get a nice high Q whompy sound in the bass. The tweeter panel will have a nice resonance around middle C you might like it! I suppose aged way out of spec original Quads may sound 'better' with the damping removed. The speaker does take a step backwards in performance. But audiophiles can be prone to doing all kinds of things that are not a step in the right direction even though they think it is.
Removing the dust covers is a very bad idea and produces little improvement in performance. I listen to them both ways for testing purposes. I can assure anyone the extremely minimal increase in performance, if any, is not worth the long term reliability issues. One only needs to look at the filth on the dust covers after decades of use to know they are a good idea. I have seen plenty of 50 year old Quads that work nicely, not to spec any more but nicely, and the reason is those pesky dust covers!
The grey paint on the front of bass panels is to eliminate glare. Rarely when serviced are they painted again. If they don't have grey paint either the dust cover has been replaced or the panel has been replaced.