I've updated the OBJ to 3DM converter (same download location which is here: http://moi3d.com/download/Obj23dmWireframe.zip) so that it now has 2 different modes that you can choose from - you can choose to either create one single line for every edge with no duplicates as it did before, or you can now also choose to create one closed polyline curve for every face.

With this second mode, if the faces are all planar than you can just select them all and run Construct > Planar to build planar faces from those closed polyline curves, then use Edit > Join to join them together.

- Michael