I would! I love coding exercises meant to gain information about a candidate; they're like yardsticks for my professional growth. I love evaluating how I solve a problem now vs how I would have solved it while interviewing for the job I'm leaving. I also just enjoy solving problems. To me, doing a coding exercise is like doing a Tuesday crossword puzzle (they're never hard enough to be stressful) that I get to show off: Look how correctly I solved this, and in ink, with no mistakes, with very well written, clear words.
I don't see it as a waste of time; it's about the potential payoff, which is a (presumably) better job with better opportunities. I wouldn't apply to a job unless I was reasonably sure I wanted to work there anyway. I might be very lucky in that I've worked for good companies in the past few years and the only reason I'd leave one of these companies is for a much much better one. Usually when I leave a job, I've become bored of the problem domain anyway and am looking to solve new problems.
Disclosure: 31 year old man, no kids, I live with my partner.