Natural resources, agriculture and industries related to such are definitely relevant to whether or not a region could justify having a tradehouse; if you build a tradehouse in a barren wasteland, no one will come to support it. Of course, abundant resources are no guarantee of a viable trade industry, either; witness Forlorn with her oodles of forestland and droves of goblyns who will swamp you to death if you try to set up a lumberjack camp.
If other domains were ever added to the server, Nova Vaasa thrives on trade with other nations (which is why Vaasi is so prevalent throughout the Core), so a tradehouse in Nova Vaasa would make perfect sense. And though governed by a pack of hyperaggressive jerks, Falkovnia is one of the Core's biggest agricultural breadbaskets, enjoys ample trade with other nations (including those whom Drakov insists on attacking over and over) and could easily justify a tradehouse or two; you just have to put up with soldiers who will try to kill you if you look at them cross-eyed, that's all.
Being a port town on the Sea of Sorrows, surely Port-a-Lucine would be justified in sporting a tradehouse. After all, if you have a ship from Lamordia selling widgets and a ship from Mordent buying widgets, where else in Dementlieu are they going to do business?