I've spent quite some time fooling around with the MoI .obj exporter and Blender. I'm now generally achieving the best results by exporting unwelded vertices and using the Edgesplit modifier in Blender. In most cases, it deals with the smoothing issues. In case you really want to connect all loose vertices (for instance if you want to apply Subsurf or Sculpt your MoI mesh), use the "Remove Doubles" command in Blender, which will merge vertices that are in the same location. I use mostly Indigo for rendering, and it is sometimes picky when rendering flat surfaces generated in MoI. A flat surface would then show with shading differences, with parts of the plane appearing darker than others, even if the Edgesplit modified is used. In such cases, the only workaround I've found that seems to be working is to extract the flat surfaces from the mesh, move them to a separate mesh object and remove the smoothing option. Curved surfaces generally don't have problems. Hope that helps.
I will now try the LWO importer and see whether it works better.