Item Vault will probably fix a lot of these issues.
Potentially unwanted Weapons/Items could be sold for gold or Smelted/Scrapped for raw material gain.
Edit: There should be an NPC item-vault. If you build a World Market (in a city) you can "buy" any items ever sold, for only gold (but a lot of gold). Plus, there will probably a few Weapons and Items from an NPC list, completely randomized ... so that if no one sold anything, you would still have some relatively cool stuff to buy.