I've got a handful of disks that are throwing errors (error 22, etc) are these just trash or can anything at all be done with them?
If the disks just have corrupt data, they could be used for rewriting. So I'd save them or sell them to someone that can rewrite.
Agreed. If you've went through and tested them and are sure the disks themselves have corrupted data you could look for someone to re-write them. Which from what I've seen from others experiences, tends to be hit or miss. Depends a lot on calibration of their drive vs yours vs factory specs.
You could always try and re-write the games yourself. I'm gearing up to do that same thing with an FDS stick and buidling my own cable. I really want to restore the CIB copy of Arumana No Kiseki that I have that some dolt overwrote with a crummy poker game
Yeah so for that reason it might be good to mark the disk as a home-rewritten disk somehow.
You can peel of the label and resuse it if you have some other game that has been rewritten.
You could also try cleaning them. Sometimes err 22 disks are dirty, although usually they are really broken.
Please try the game in another FDS before you rewrite it! It may be your drive that's bad (some disks are easier than others so a slightly-off FDS works with a Mario or Mahjong and fails with a Zelda...).