Hmmm...guess I don’t have as negative a view of student evals as you do. I agree that, often, a majority of students don’t fill them out. Also, those who do often either really like or really hate the class. You can always recognize the latter as they just mark “strongly disagree” for every question. Some of the qualitative comments are interesting to read too. Still, I do find them valuable and they are generally what I expect them to be (but not always).
So, on average, I find them to be “fair”. Still, not everyone agrees with me. A number of my colleagues also have a negative view of student reviews. Where I teach, once you have tenure, student reviews are optional unless you are under evaluation (every 4 years). Still, I do them every semester anyway because I want to see what the students think.
I still say to do accurate evaluations, you need to have an unbiased third party (neither students or peers). However, finding one that is truly “unbiased” may be quite the trick in some disciplines.
My evals are generally very positive but I also have many that are unfair attacks. Thing is, my ‘leadership’ focuses on the odd eval that falls outside the statistical norm and treat that eval as objective truth that indicates an issue to be addressed.