sakura This is my point, I don't see why they need to be useful if the droprates are already good.
If the junk items are given are given a good use (ie turning them intro desirable polluted items) then you'd be required to autoloot them and turn them into polluted spirits to have maximum farming gains.
I don't want to need to loot 8 new items into my inventory that look and sound similar to each other and other items the mobs drop, that sounds like a major hassle and I don't see why it'd be necessary to implement.
I'd rather junk items just stay junk items so I don't need to nervously shuffle through my inventory trying to count them after each session to load them into an npc to turn them into useful items; when I could just farm the useful items directly.
By making them important crafting ingredients, they become mandatory items to loot and hassle with.
This is why I mentioned increasing the drop rate, if you want more polluted spirits from the dungeon then increasing the drop rate would have the same outcome as this suggestion but without the looting & npc hassle.