I think "being productive" vs. "time well spent" and "doing things that really matter" is a false dichotomy. It doesn't have to be this way. I know that's a statement from a position of privilege— not every has a job where they can feel like they are in a flow state while working, but do you have any side projects or hobbies where you feel both productive and feel like it's time well spent?

Coming to this pretty late, but I've been fascinated with the concept of flow recently, which researcher Mihaly Csikszentmihaly described as:

  “The best moments in our lives are not the passive, receptive, relaxing times . . . The best moments usually occur if a person’s body or mind is stretched to its limits in a voluntary effort to accomplish something difficult and worthwhile”

Again, not everyone is in a position to do this, but I think we should de-emphasize number of hours spent in "work mode" albeit inefficiently or without great focus or working on things that aren't super important and more time seeking deep focus and then time completely off to relax, recharge and let ideas background process/percolate.