Dont smooth the mesh in one single smoothing group it only works for sphere like objects. Smooth the whole object and select the edges with a very strong angle and make hard edges.
Yeah i switched back to World Space and with a bit of tweaking it works. Object Space is taking object scale into account. I'll post my solution which is basically the same as yours.
just a quick shot is it really invisible or is it inverted? rightclick your object in max go to object properties and turn backface culling on, how does it look then? if thats not it, make some screenshots :)
You could try this: duplicate the model, edit using Symmetry, then copy the Unwrap modifier from the original object's stack to the new object. Dunno if it'll work but it might be worth a try.
Question: are those merged into the same object or are they separate objects? I'm frankly amazed if you got that many polygons into a single batch without hitting big problems.
One main problem you are facing is that you created everything as ONE object. Try to seperate the scene into smaller objects. So you are able to reuse parts of it.