Energy Credits used to be energy and also currency. It's in the name. Now it's been relegated to only being used to power robots/factories and little else.
Trade is the new currency. Currency is the medium of exchange used when buying and selling.
But Trade isn't just a type of currency, Trade is ALL types of currency - fiat money, commodity money, representative money... barter, honour, time, psychic power, etc.
All the places where the game thinks Energy Credits still exist in their old form, or that Trade doesn't exist feel confusing and messy.
But Trade isn't just all types of currency. It's also fuel for the Borg, shipping volume for trade fleets, the flow-rate of capillary towers pumping mass offworld for Zerg/Tyranid and even just a vague debt that needs to be repaid for a warrior culture. It's also the only representation of the private economy, untapped resources and increasingly inefficient mineral deposits not normally worth harvesting but possible if you don't mind the inefficiency. It also seems to be like the Ork Waaagh! So now my Ork-like Civilians can make shipping containers fly if enough of them believe that red makes things go faster, so who needs alloys, engines or fuel to supply planets?
It's hard to try to squish so many different meanings into a single number and have it make any sense.
Personally I'd rather have:
Energy Credits as currency used on the market (it already works)
Trade goods added later using a modified specimens system (named goods, each with flavour text and unique benefits)
Logistics folded into naval capacity. Planetary Deficits use naval capacity, going over capacity increases upkeep costs. Freighters/ports/anchorages add naval capacity.
