Huh?!?
Sounds like you've got the tail wagging the dog there. Badly designed software is not an excuse for not adopting industry standard conventions.
What is a westing?!?
Have you ever used westings? Distances would get smaller (or negative) the further you got from the origin. Sounds absurd to me.
If you are modeling a mechanical component that can be mounted any way up, XYZ co-ordinate orientation is irrelevant. However, if you are modeling a hotel or an industrial process plant, XYZ consistency is imperative for reliable interaction of the various engineering disciplines & contractors.
Importing a correctly orientated inventor model into a navisworks file already populated with correctly orientated autocad components that ends up laying on its side is a major flaw that should be addressed post haste. Co-ordinating models from different applications is supposed to be the whole point of Navisworks is it not?
Three expensive Autodesk applications that don't interact properly. That is an embarassment.