danr: First image, the bright yellow thing as sometimes referred to as a truck.
WayneAdams: Saturation never hurt anyone and is totally valid for anyones portfolio. Poops right, I'd fix the satuation levels up as it isn't exactly consistant across the entire shot. Like I said though, saturation never hurt anyones portfolio. However, the piece has to support the colour values and I don't believe your subject matter and its artist style do this. I hope you don't mind but I spent a few minutes at lunch to do some post-production work to your image to show you how much farther you can run with this.
I desaturated the colour of the overall render slightly and changed the colour of sky to a more orange colour to help that skiddish feeling this set gives me. The sky was then desaturated further than the rest of the render. A vignette and colour noise was added to help the aged look of your scene.
Personally, I don't think doing post-production work does any portfolio harm. I believe it helps hugely if the first image they see "wows" them. Using some post-prod lovin' can do exactly that waaaaaay more than some in-app only renders (whootpy-doo). I'd try and make sure everything you doin in post-production isn't anything different than what games are doing these days. Everything I did to the shot, save the sharpening, is being done in current-gen titles. If you go this route, show some technical shots and texture flats as well so future employers can see that you've got the execution know-how to go along with some fancy Photoshop skills.
Hope this helps.
Let 'er rip!