You say that when you export an obj that had previously been imported into Vue it gets messed up.  A couple of things:

1. Vue triangulates all imported meshes.  So if you imported a an object using quads it will export using tri's and they won't be welded either.  You may have to use something like UV Mapper to weld the mesh.

2. UV's and material zones may also get screwed up after export if you use exotic procedural materials. 

The Vue exporter is really designed to export Vue objects (e.g. Terrains, Vegetation, primitives, etc).  It was not designed to re-export objects which you have already imported - although with a bit of work, this might be feasible in some cases.