Relatively low Quant score an issue for INSEAD?

Good question, Will! I'm inclined to answer your question with more questions:
1) Do you believe that you underperformed on this test, given your own background and practice test performance? Or do you think that was the best you could do at that time? I find that most people can give an honest answer to this question, and whether your score is due to knowledge or to test-taking skills will make a difference in how well you might perform next time around.
2) What was your major in undergrad, and how much quant coursework did you have? How are your grades overall, and how were your calc and stats grades in particular?
3) What are your career goals?

I think you can figure out why I'm asking these questions. Some employers take strong GMAT numbers into consideration when assessing potential post-MBA employees, while in other career choices it's not a factor; schools consider your employability in your chosen field, among many other factors, when determining whether you are strong for their school.

Hope this helps, for a start.
Margaret Strother