In the 90's the C&S stuff went for a decent amount but in the past few years the market for it has dropped to almost nothing.  That goes for most of the FGU stuff, which is a shame since some of it is quite good such as Space Opera.  

C&S was always a bit rules heavy for my tastes, and if I want Arthurian fantasy role-playing then I'd go for Pendragon, which is superb as Chaosium products usually are.

I have the entire collection of C&S 1st edition stuff now. I just picked up the old Saurians supplement. I still think that Land of the Rising Sun is the best Japanese RPG ever.

I just don't think I'll ever play it again, as my tastes in games have changed toward simpler systems, like GURPS or Unisystem or Tri-Stat.