Maybe add a couple speeders jacked up on cinder blocks 'cause their repulsor units have been ripped out, or even some low-poly refuse heaps (similar to what's in the first part of the Baron's Hed level in JK) or a couple overflowing dumpsters could help give it a more lived-in and dysfunctioning city feel.
Also, you could do stuff like if you decide to have street lights have a couple blocks where they either don't work at all or flicker, or are real dim, same with interior and exterior building lighting and street signs. You could also use textures to make boarded-up windows and doorways, and some blaster burns in the sides of buildings, especially in alleyways.
This is more for actually using the level: While the engine probably wouldn't allow many at a time you could always add in groups of tired, poor and huddled masses, too, or toss in some street thugs that are willing to attack anybody. Nothing screams "Crumbling Social Structure" like the Sharks and the Jets squaring off on the West Side. Talk to my friend Mr. Bernstein, he could help you choreograph it.
I do have a question: What levels of the city is this map supposed to be at? The upper levels would be a lot less decayed with things getting nastier the lower you get (Now trying to accurately render the SURFACE of Nar Shaddaa, THAT would be crazy).
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[This message has been edited by The Saxman (edited June 12, 2003).]