Yes they definitely sound superior, overall clarity is much better, the bass is much more detailed and tighter, the highs are crisp and clearer. To me the difference is more notable on the Illusion's than the other two.
The MFSL Ultradisc CD's are regarded by audiophiles around the world as being among the best quality and best sounding discs available.
Obviously as Dash_X pointed out the better your HI-FI system, the better the results, probably would not make much difference in cheap and nasty stereo systems.
But how, how on earth can this be? I mean, the information is digital, you can either read it, or you can't. And if you can't it's gonna be fucked-up and if you can it's going to sound like it was supposed to sound. The digital world is really simple, it's true or false, there's no in-between, and there's no maybe. The gold plating can account for durability, less wear-and-tear; but not for clarity, more bass, or whatever. It just does not make sense, it does not compute!