I think it would be good to link the experience gained for trading to the profit you do. So buying 7 pieces of X for 10c and selling them for 1000c would give you more Exp. than buying 22 pieces of Y for 9c and selling them for 10c. Cause actually it's the profit that makes a good trader and not the amount of cargo he ships.
This would also include adjusting the Exp. for selling the different ores. I think it's not logical to get 3 points for Carbonic Ore and the same for Heliocene.

greetings
crazy-daddy