what is killing your sketches are the proportions. They look like micro machines because they are very short. I took your last sketch and skewed it, worked it, and liquified it into a supercar proportion. Same sketch, just changed the proportions.
Also, if you want to get into ACCD or CCS, they are maniacal about presentation style. Work on getting your scans and images of your sketches as clean as possible. I had a friend there who had to do an entire assignment over because he smudged his signature on the sketch.
