Incentives for Course Feedback?

I work closely with end of course evaluation surveys.  At one institution, I administer the online survey system through which we survey students, and for the other institution, I rely heavily and place high value on feedback from students to help me continuously improve the course.  My question is, “How much is that feedback worth?”Based on research in the field and discussions with colleagues, the greatest influence on student motivation to complete end of course evaluations is the student’s belief that the instructor/faculty values the feedback and will actually use the information they provide.  The second strongest influence on student motivation to complete a course survey is a local incentive; an incentive specific to the course like extra points on an assignment or as a separate class grade.  Other factors could be global incentives like entry into a college wide drawing for a particular prize; many institutions have given away iPads or netbooks or other gadgets; one with which I’m familiar has used scholarships for the next semester.

In discussion with colleagues, faculty have differing opinions regarding the validity of local incentives that have an impact on the course grade.  The argument that completing an end of course survey is not a valid assessment is quite accurate; in that instance, a portion of the student’s grade is based on something other than their performance in the classroom.  I absolutely understand and respect the argument.

With that said, if I can go from a 16% response rate to a 90%+ response rate just by offering extra points on the final exam, is the feedback for me not worth giving students a bump on the final exam?  If the extra points amount to a 1 point bonus on the course average? a half point?  1.5 points? 2 points?  What’s too much?  We are talking about a significant source of “quality control” for the course?  The teaching and learning environment I provide and facilitate is the service I’m providing; the end of course evaluations are a source of quality control for that service.  How many extra points is it worth to get feedback in a single section from 24 students rather than 4?

Your thoughts?