From all I have seen of your work on DVA no doubt this is your strongest talent, If I were you I'd really focus on these kind of things, great work, I'm going to watch you- I hope to see much more mechanical design from you in the very near future!
I never understood why drawing silhouettes is so popular, especially between those 'experts'. I do realize it's a way to play with ideas and shapes and all that, but I always valued good line art sketches instead, they seem to show so much more quality. But I guess it's just me, not knowing how everything is. Though most of the artists do both of those styles.. You will be better at it, if you think you are not good at it already ^^