Replacing or redoing the meshes is unlikely at best. We lose so much when we bring existing area models into Max; lights, lightmaps, walkmeshes, effects, emitters, etc.
I'm not sure that the improvement would be worth the time that it would take to re-create all of that. But, if you find a way, more power to you and I am more than happy to answer any questions you have in that area.
I think the work you're doing on the textures is fantastic, and I'd love to see all the planets done in TSL and KotOR in similar fashion.