The big bonus for a MT is it pools the ore you have on that planet with the ore on every planet with a MT. Also keep in mind the traders goal is to acquire the ore, not maintain it. So spending the 4k RO for a MT doesn't matter in the long run. It will just allow you to build cargo ships and things at newer colonies.

When you build something on an MT plant, it takes the ore there, and then starts looking at the other MT planets for ore if it requires it.