1. Most MSFL gold CDs are redbook CDs (excluding newer SACDs of course). I believe they've all been re-mastered. MFSL produced aluminum CDs as well as gold CDs.
2. There have been 2 MFSLs, the original and the current one owned by Music Direct in Chicago. The vast majority were manufactured by the original MFSL. I believe the original went out of business. A few titles have been released by both entities.
3. Generally, IMO they sounded better than standard releases of the same titles available at the time (I've owned many over the years). However, in many cases even better sounding versions have subsequently been released. I also own several newer MFSL gold CDs which sound excellent.
PS: I don't believe I would pay $500 for any CD.