Nah, no special currency related to weapons yet.

Obsolete weapons do still have a use though. Once you're sure that particular weapon will never be equipped in any of your weapon grids, then it's basically meant to be used as fodder for skill leveling. Skill leveling is something that you won't completely finish for a long time.
(except N's. N's don't contribute to skill leveling so they're trash meant to waste your time enhancing/selling away)