You might want to set the brush on antialias when you draw lines..it makes them less scratchy...looks like you're starting to get ahold of the tools

Yea..it's coming along.. try not to use the blur tool much.. it overdoes stuff..like in the rims...looks good so far

3 things I think will make this stand out even more and make it more realistial. 1. on the wheels.. do a strong highlight on the bottom outer ring of the light grey part and the darker grey triangles.. maby darken them and darken the top part of it even more.
2. On the rear fender.. maby add a slight highligh on top of it right under the window piece and on the door darken just slightly where the fender sticks out on the side just a bit. It will make it more 3d looking I think.
3. The back end.. maby raise it just a bit.. and the red part it looks almost awkard slanted with the grey part. If you made the red part straiter up and down and left the grey that slant, and raise the rear spoiler up a bit more i think it will work great.
You have a great start so far and I know how hard it is to make cars look real. Trust me I have done many vehicals. :)