I don't think headphones really have much resale value overall outside of a few specific models. Wires get loose, the pads and strap wear out and the industry is constantly releasing new models so once something falls out of the spotlight, I'd say most anything over 5 years old that wasn't a smash hit, it's probably not going to sell for much. I got my favorite pair of Sonys for $100 because it was a model that never really took off 10 years ago. There's also a lot of Focals out there, I probably couldn't get more than $200, maybe 250 for my Elegias. It doesn't help that the Focal suede/velour pads show age poorly.
