All hail the sherpa! Why is it that there are always exactly seven comments by the time I get to your posts?  New goal in life: be #6.

Quick thought: when I remember myself as a child and the various things I "endured," I am struck by how little a concept I had of "being grateful for it later," of a "long-term" future in which I may be glad I had to do Activity X.  Heck, I even look back at some of my college classes, thinking, "My prof was right--I should have been collecting my work for a portfolio...I never would've thought..."  Which leads me to believe that the, "you'll be glad when you're an adult that you did this" thing isn't great at motivating.  That being said, you still have to say it, because you want your kids to grow up and be all like, "Man, Mom and Dad were wise...I'm never going to tell them they were right."

One thing that I think does work is leveraging peers.  My best childhood friend had no interest in music until I started playing the flute---then she was all about it.  I almost dropped out of my watercolor classes--until my mom set me up on playdates with other young painters.  Suddenly I belonged somewhere--I had peers who were into it; and maybe it was a little bit of a competition, too.  And so the incentive to do it suddenly became my own, and I was motivated.