Considering that salt was the primary means of trade through most of human history, it really should be worth a whole lot more up untill refrigeration removes the need for it.
I mean the word salary comes from salt... It basically means "salt wage", because soldiers got paid in bags of salt, which they could bring with them everywhere and trade with the locals. Everyone had a use for salt. It was litterally worth it's weight in gold...
Today it's mostly a basic spice, but back in the day it was the primary way of preserving food long-term, the other ways being drying and smoking.
Medieval nations like Hungary and Poland grew strong from their access to major salt mines, while the North Sea peoples undermined whole coastal regions digging out salty turf.
So my suggestion is to massively increase it's worth in game, at least to a level on par with gold and honestly probably more. And then take most of it's importance away with refrigeration.
And don't get me started on the importance of norwegian dried fish in forming the Hanseatic trade league (which grew big on controlling the salt trade btw.)