I'm not exactly seeing this as a "make trade goods before we have a trade route" thing here. Local production is valuable in that it:
-Produces an export before the major trade route is set up. Which means we get lesser trade routes starting up. Yes, it wouldn't be especially unique, and thus would not be trading long distance...our immediate neighbors are not going to be disconnected from us due to provincial politics(which we know some upheavals are coming).
-Bolsters the value of local production. Remember those spirit plant seeds we have? Would be nice to have them refined into pills locally, or at least more compact extracts before we export them, because that way you get more value per cargo space, or even use them locally to bolster our forces. Same with any local animal or mineral products.
-Provides a local source of essential equipment, we probably should not be importing rank and file equipment and wards if we can help it, and nurturing local producers is a key element of not having our equipment traveling in shipments that can be raided or robbed easily.
-Processing goods before they head on to their final stop is pretty lucrative. Sure, far southern iron is valuable, but we'd make more if we had them refined locally into tools and equipment before selling them further north, and likewise, if we have the local crafts capacity, wooden crafts would sell for more per cargo volume than bulk logs. It is unlikely that we have the capacity to convert the entire shipment, but every bit done is a profit.
Now whether this is as valuable as ensuring that the trade route holders are on board with the new route rather than looking for ways to sabotage or get buy in, is up for speculation. But this isn't entirely about trade goods or happy craftsmen.