I still think Culebra should be the primary offloading point for Scrap Metal.
Shipyards aren't going to want random chunks of metal mixed in with a heap of other crap. They want steel. Plates, rods, flatbar, tube, angle-iron, so forth.
Culebra takes the scrap, smelts and reforms it into something that can be sold. A new commodity "Steel", which can be sold to a wide variety of stations with prices increasing proportionately radiating out from Culebra.