CD32's didn't hold their value very well, imho. Even in my neck of the woods (Canada), where they are fairly rare you can generally pick them up with a couple games in good condition for $100. That being said, there's still a fair demand for them from collectors that like to have "one of everything" Amiga wise, so they generally aren't too difficult to sell if they are in good working order.
The SX32 add-on however, that's a pretty desired bit of kit for them, especially the high end SX32.