Why a spiritual practice?
Because you're alive, dammit. Do being alive!
It's living well that doesn't cost a dime. True, you'll probably not have your own section of schlock to hawk in Macy's but you will live better than you can imagine Martha Stewart might.
Why do I do zazen?
Yeah, like Warner, I feel worse when I don't do it.
The practice helps one to replicate thinking patterns that happen throughout the course of the day, when it'd be really advantageous to actually be a "zen master" instead of simply playing one on a cushion.
Evidently though, you've got to play one on a cushion in order to be one at the most critical and mundane points in your life.