I never did any resistances upgrades until I was ready for the final battle. Just never found enough of those things to use all the time and I wanted to make sure I had all the resistances I could for the end boss. Armor just changes why too much while I'm leveling up from loot finds so I didn't want to upgrade that stuff other than just non-resistance upgrades.
LeBurns has a great point, save your rubies for items that you will never change.
In my coop game Jahan is practically made of rubies (he is carrying about 10-12) and i used only 1 in my sarong (which i don't intend to change anymore) so far.
