I like this question, it brings to fore some of the possible game mechanics we may see in the future in relation to what kinds of cargo a ship might carry.
We know the intent is to build up cities that have been destroyed in the various faction wars, I can assume that valuable items may come from a long ago proposed crafting system if we consider crafting in tiers as follows.
Raw Resource<Refined Resource<Manufactured Parts<Assembled Goods<Refined Goods<Luxury Goods
There can be a lot of branching from this idea into various items that would need to be delivered to a city for the city to develop and evolve it's assets and defensive ability, improving the value of the actual city, or improving the kind of goods the city could produce.
With this previous thought we could see a chain of cities developing different parts of the chain of goods, making every resource more or less valuable in the city that it is sold in.
In Anvala finished goods would be required to assemble Superior goods, to be sent to Sanctuary to be refined into Luxury Goods. Superior goods would be worth less in Sanctuary than they would be in Anvala, but Luxury goods would always be worth more than anything under them, but the best prices would be fetched in cities that consume Luxury goods, and not a city that refines raw material at the bottom of the chain.
We could expand on this even MORE, have entire unique lines of goods that require precious materials to start the initial chain, like gold, or silver, making those raw resources almost as valuable as Luxury goods of inferior material, but items that would still be less difficult to produce in quantity making them smaller profit margin, but safer investments from piracy.
(I put my EVE online hat on there for a moment.)
And then there is Skywhale oil, the most precious resource of all.
