I have had mods done to my SFCD-1 by Pcx, everything except upgraded tubes, which I already had. It was absolutely worth it. An already excellent CD player jumped a class. I love this CD player (always did), and have no plans of future upgrades (to another player). In fact, it is the only component, including cables, that has not changed since I got it. I also had the laser assembly replaced. These do not last forever. I have a fully-modded (Modwright) Pioneer 47Ai for DVD, DVD-A and SACD duty. The Redbook playback is actually pretty good with this unit, more dynamic with better bass, but not near the level of refinement of the SF, particularly in the mids and highs.
I had it done a couple of years ago, and I no longer have the itemized receipt. I do remember, though, that a lot of it was replacing Capacitors and Resistors - lots of Riken, Black Gate and Auricap.