I messed around with your file a bit:
And I produced a couple of renders. One is the full body shot that you set up, with ray tracing. The closer one is a scanline render with approx. ambient occlusion.
Your model was quite polygon heavy and used a lot of subsurf. Some areas had uneven distributions of vertices, e.g. the pipes had a lot of vertices defining the cross section, but very few defining the curve of the pipe, so adding subsurf was necessary to smooth the curve, but added a lot of extra vertices around the pipe.
I reduced the amount of subsurf on most of your objects, or removed it completely if it didn’t make a significant amount of difference. I added the edgesplit modifier to everything, to bring out the details. Stupidly, I applied the mirror modifiers you had on everything (I don’t know why I did that!). Some of your objects had doubles, so I removed them.
Hope this helps.
[edited to change pngs to jpgs]