I'd rather like to have to upgrade citadel to allow you to get higher tier levels. So, one hero must be the one farming for their partners to get chubby.
SKILL: The Armory
Lvl 1 -> You get Lvl2 Tier items.
Lvl 2 -> You get Lvl3 Tier items.
Lvl 3 -> You get Lvl4 Tier items.
Lvl 4 -> Items cost halved.