There should be currency sinks.

Let us donate material to add bonuses to squad impact. Or receive buffs or something.

For instance you could have a set amount required to add SEAF support to a planet, or an extra stratagem. This would even let players bank defense on inactive planets.

Yeah being capped out sucks. My monkey brain demands rewards!

I would gladly convert my super rare or rare samples into common samples if there was a way to do it.