Stars Without Number follows this model, as do I these days. Only the newest/poorest of colony worlds needs to import much in the way of manufactured items. Most of those would be high-end gear which their minifacs couldn't make from local raw materials (e.g. they had not been pre-loaded with the correct highly-expensive copyrighted templates). Everything a trader physically carries between worlds is going to be low-bulk, high-value luxury goods. In short, I mostly have a low-trade, small-ship, relatively-poor-Imperium TU.