Thanks for your comments on my work. You asked for some commentary on your gallery, so here goes:
I prefer your earlier style where you were creating abstract motion backgrounds to your current photo integration. Without lighting, reflections, and 100% correct perspective, that marry the two images, the vector illustration contrasts too much with the photo style. In the end the cars look like paper cutouts and that detracts from the work and skill you put into them.
My favorite is your Silvia Showcar. I like the color and the simplification of the highlights you've achieved. I even like the light effects, which usually turn me off.
You gallery shows improving skills, so keep at it. Your lines and selections are getting smoother and more skilled, so you're really on the right track. I suggest your learn the pen tool for creating selection sets. After some getting used to it, it's easier that your current method an provides far superior curves and lines. I'd also suggest you abandon your stylized "two stripe" windshield reflections. They look odd to me. The windscreen usually reflects the sky dome or adjacent structures. Your glass seeming reflects two bright white linear objects in the sky and I'll be damned if I can guess what they'd be.