Not really convinced about the added resistance.
Also the noise of mechanical keyboard is meh.
The Dell keyboard at work already makes too much noise when typing on it. =/
I saw somewhere that you can use dental elastics (the kind used for braces) as a keystroke dampener to mitigate the contact noise of key on backplate. If you have a mech switch type with an actuator click, not much you can do.
There are also specific O-ring kits for mechanical keys, but I'll be surprised if we can find those in SA.