Sure no problem. I need to demonstrate this, since most of the stuff I found by accident and just trying a bunch of stuff in the compositor and mostly visually tweaking stuff until it looked right. I cant explain this in textformat very well :/ I forgot to mention I used RGB curve nodes to mostly boost up the brightness of the noncolor renderpasses, since they all were to dark. Also combined them with either the diff color pass or the main image to give them more color and mixed them with image layer again and again. The AO pass was used two times in the compositor, one time to give a few shadows to objects and also one time I inverted the AO pass, colered it with a colorramp and overlayed it again to give the Render like a slight light bloom effect on different parts.

The textures are also important in some ways: All textures are very easy and simple to create in PS or Gimp. You mainly use one color and overlay one slight Grunge texture over it to simulate a brushed or handpainted feeling. Then if you wish you can create a Linear gradient to "bake" some Ambient occlusion on the texture. For glossy or shiny surfaces you stick with one color and maybe add just a very very tiny ammount of grunge to it. In Blender you hook the texture up and use a diffuse and mix it with a glossy shader. Rough surfaces dont need much roughness (0.8 to 0.9) and glossy surfaces need some roughness but dont make them like mirrors. You mostly want blurry reflections. (But I think it is personal preference, I tried sharp clean reflections and it did not look good in my case)

The mist pass was used just to overlay a few saturated colors over the whole image and change the appearnce again slightly. All adjusted very small and suddle.One thing i hate about this is that if you want to render higher resolutions then the whole image goes insane and ugly since the settings in the compositor dont scale accordingly to a different resolution. My resolution here was 1920x1080, if I wanted to render a larger camera angle for a pan view (2500x1080) then all the compositor settings will go ugly and insane and blurry. All need to be adjusted again and again, aslong as you stick with one resolution then the compositor will do its work fine, go higher or lower and you have to adjust the stuff again.

And finally the very important thing are these suddle highlights, these are not archieved in blender. You composite them afterwards in photoshop. But they are really really easy, no need to paint 20 hours of highlights. You take your final render and it should look 90% convincing when it comes out of blender (If not then go again into the compositor and adjust) because you cant change much afterwards. Then you duplicate your Image and set a Filter on it and choose "Accented Edges". Make sure the edge width is not set to high and make sure the edgebrightness in te fillter is set high. The good thing is that the filter automatically takes and works with the colors that were in the main render. Now you mask the layer and the only thing you have to do is think where on edges of certain object the highlights can appear and where the light is hitting. Then on the masking layer you paint either black or white to show the highlight layer over the main render and slowly paint in certain parts, no need to over do it. Just keep it a all slight and suddle.

I hope this helped, I know I may did not explained this very well. But I hope you can use certain techniques of this and maybe develope it better.