That's some great looking city terrain! It already LOOKS good, and the low walls and different surfaces give nice variation to movement and partial cover; the one thing I would say it is lacking for 40K needs (and other games I expect) is large, Line-Of-Sight blocking terrain.
Armies like Dark Eldar and Tyranids need solid terrain to hide behind if they are to survive the first few rounds of shooting, so I think you need to incorporate some buildings that fit in the gaps. GW's buildings might be a bit too Gothic to match your board nicely, but what about:
http://www.antenocitisworkshop.com/antenocitis/governance-of-technology-got-scenery-1.html
There are a lot of independant mfrs doing laser-cut MDF, molded or cast future-city scenery that I think would suit your style well, be it buildings (which might be tricky to fit in the gaps without looking too small), or shipping containers, Industrial plant, or advertising hoardings.
Another other thing I saw at a convention yesterday is big chemical fires: a 6" wide 6" high 2" thick block of blackened cotton wool, with several flickering orange LEDs as it's base, could count as a ruptured pipe, impassable and impenetrable.
Subject: Modular Cityscape 
Sun Apr 21 2013, 00:59
