Orbs take up a lot of backpack space, as they should. So when someone like me suggests adding new ones, you're bound to ask "how can I carry more?"

So lets have an alchemist who can combine the power of your orbs to raise their potency. Trade 2 simples for a lesser, 2 lessers for a powerful, and 2 powerfuls for a flawless. It will still cost less to purchase the level you require, but if a creature or a quest reward gives you an orb that would create a new "stack" - you can simply combine it before you move on.