I found some (set of 4) genuine "Moon" discs on eBay a couple of weeks ago, 13", and got them for $50 including shipping. One has a little dent and one has a scratch in the clear coat, so I figure that is quite a deal. Put them on our 2000 Metro and they look great. Not sure if they make a measurable difference as I have no way to tell, yet, but I was missing a hubcap anyway, so thought these were worth trying.
Now I need to get some "Mooneyes" decals, and maybe a Mooneyes tee-shirt for my wife.
Dispite having smooth hub caps, front and back wheel well skirts, exhausting my radiator air into the front wheel well and doing a lot of mountain driving, I have not had any problems with brake fade or warped discs.
Most discs get warped when someone does a lot of hard braking and immediately afterwards sits for awhile stopped at a red light, etc. with the hot pads clamped down on the disc so that the clamped part of the disc heats to a high temps while the rest of the disc is cooling down. If you have to stop after a lot of hard braking, it if best to hold your position with the parking brake or with the auto trans in "P", rather than sitting there holding the brake pedal down.