Glad I can be the measuring stick against which your work is judged.
One quick question, do any of these pieces include a door for workers/employees?
If you take away nothing else from my models, pay attention to proportions and how subtle change in the texture has a big visual impact (Miller St could have been better in this regard). If you add a blotch or stain, try to tie those changes in texture to something in the surfaces' surroundings or sensible wear (like a low spot along a drainage path). You do not need to have a really dramatic change in texture (that is, contrast or color) in order to have the desired impact. Also, try adding some noise or try re-sizing textures so that you don't end up with faces that look like a flat color. With reinforced concrete industrial buildings this isn't easy to do, but look at Fisher Body 21 as an example if you need to.
I have one other texturing note; in the BSP*, we always calibrated our color palette against similar Maxis buildings. I think a similar approach may be helpful for you.