Actually, I've heard just the opposite...that is, student evaluations are essentially ignored. Perhaps if an instructor is being considered for a professorial position, but other than that profs are usually bulletproof.

There was a real bad prof at my old school, and every year her class organized a petition to have her removed. She finally did go, but not because the administration did something...but because she had a nervous breakdown over the petitions! Real irony, that.

Having said that, an individual student can often fight to have his or her grades changes. So Taonuviel, even if the procedures you have to go through are complicated, go for it. Often making as much noise as possible is the only way to get things done, but if you're in the right, and it certainly sounds like you are, things do often get done.

Keep us posted on how things are going. Good luck.