This may fall under Maha's earlier suggestion, but i came across the thought that, for gold bars, a player could set up a tavern in a port, upgrading this tavern with gold bars would increase influence a bit(happy if this isn't a feature), make hiring crew cheaper or make the product cheaper. I'm happy for any of these, but it could be that the player chooses what effect the tavern has on the port. Having it cost Gold bars would also be a nice feature that makes G.B's a higher demanded product, but also ensures that it's not too easy to set up a tavern or upgrade it.

we need a ton more things that add goldbar costs