Yup. I'm an ex-mountain biker as well. Used to live in Vermont and skied and mountain biked like crazy. Those adrenaline rushes accelerated my introduction to Curezone :)
Yeah you are right that some purists can be quite dogmatic. It's so ironic because they can't see their ego is creating their firm views.
A little mindfulness is better than none. :) It would seem that if you spread those 10 days over a longer period of time, with some contemplation in between, it would work just as well.
Sure it takes longer, but it's just like any other skill. If I practiced golf for 8-hrs per day, 10-days straight, I would improve faster than if I practiced once per week for 4-hours. But once per week is better than not practicing at all.
I like a lot of John-Kabit Zinn's stuff. He has stripped a lot of the Buddist traditionalism out of mindfulness practice so that anyone can use it.
This is an outstanding type of meditation. He calls it True Meditation. It is very similar to the "just sitting practice"