My methods may not translate well, as I have a rather backwards approach, but I do have a few suggestions...
1) When I'm doing super-smooth metallic surfaces, I never try to portray the texture of the metal, rather I let the reflections do so for me. In your photo, both the kitty and the jaguar give great texture to the bonnet itself, as well as defining its shape. Large areas of smooth surface are quite difficult to render consistently, so I tend to go with a less-is-more approach.
2) For the areas that must be scratched, or for a more photographic approach, as you'll see in the pic above, I tend to use my fibreglass brushes for the best compromise in tonality and texture. I will warn anyone new to the FG brush of two things: a: it takes TONS of practice, and b: vacuum your workspace constantly. One little fg filament embedded in the soft flesh under your eye is enough to last you a lifetime.
3) For the brighter areas like the upper right corner of your photo where the light has almost whited out the metal, I would very carefully clear the entire area to white and add layered washes back in, scratching out my highlights, to get the tone I wanted. There are many areas on this next image where I took that approach.
There's also a good object lesson in this piece, as you can clearly see in the fender area where the clouds are reflected where I scratched too deeply as I was clearing the board. Use gentle strokes or a very fine steel wool or sandpaper, or, no matter how many folks rave about it, you'll always see what you consider this huge black eye in the piece.
4) Lastly, I usually mix all of these concepts in each piece, and the result can be pretty cool. Just remember that my answers aren't necessarily your answers, and I still find myself making it up as I go rather than using any special "technique":
Whatever you do, you've chosen a terrific photo to do, and just have a boatload of fun with it!