Exchange Surplus Weapons
Having earned all possible power gems, I have spent lots of time just running around, collecting items, and using them to make weapons for any future battle runs. However, I'm sure that there are at least a few of the HUNDREDS of weapons I have that I won't really need.
Perhaps a feature could be built in that allows for the exchange of weapons from one's arsenal (or closet, bunker, chest, etc.) for either Wumpa fruit, trophies, or even purple crystals? I think it would give more reason to keep making them in the mean time.