I'm gonna try 2 LOD. It's not going to be that much more detailed so it wont help performance much, but It's just to try. As for the windows, if i make them transparent, all we'll see is an empty building through the windows so i'm not sure if it would improve the visual... ![Undecided :-\](http://forum.outerra.com/Smileys/default/undecided.gif)
... not sure in this, but maybe an environment map "mimicking interior" ... have seen that on some games. But, im still think that glass reflection could be enough - but if its your model, you can put the 3DMax/blender file and maybe someone picks on the interiors too ...
Yes, pretty much something something ala EDF2025. Couldn't find a good picture, but this video shows the details on the buildings:
[Watch @ 3:18, 4:01, 4:29]
Basically what you described, a small simple interior textured behind the glass.