Which weapons are worth upgrading in Expedition 33?

Upgrades cost Chroma Catalysts at the Curator in camp, and the higher tiers get scarce, so don't spread them around. Pick the one weapon per character whose passives match how you actually play them and pour everything into that. A weapon you'll swap out in two hours isn't worth a single catalyst. Also check what element each weapon carries before committing, a big number on the wrong element is useless against half the bosses.