The authors mock the What Color Is Your Parachute approach of establishing a clear desired vision, and urge instead an aggressively flexible approach of constantly rethinking your priorities, which to me sounds like an awful lot of work.

I think that depends on one's natural inclinations. I'm personally incapable of forming large life goals, so my whole life has been an iterative process:

1) Do a thing.
2) Do I like doing the thing?
3) If yes: keep doing the thing. If no: pick a different thing to do.
4) Goto 1.

This is how I approach work (my average time at a job was less than a year until I found one where I was consistently happy, and I've been there eight years now), relationships (often explicitly on the basis of "We'll stay together until we don't feel like being together anymore"), school (which is why I dropped out three times), hobbies (I have a knitting/cross-stitch/origami/reading rotation), and so on.

I only check in with myself every few months, so it's really not a lot of work. Certainly it's much easier than continuing to do a thing that makes me miserable. I have no tolerance at all for misery. Once a thing stops working for me, I make sure it's inherent to the situation rather than temporary, and then I bail.

I intellectually understand that many people have goals that motivate them to, e.g., suffer through years and years of higher education and crappy low-status jobs even when they feel utterly wretched, and that once they've reached their goals presumably they feel the suffering is worth it. However, my iterative process has brought me to living in a gorgeous home with a marvelous family, a job I love that pays me well, friends I deeply trust, and all the other things that are supposed to justify years of goal-driven scutwork--and I spent those years actively caring for and supporting myself by refusing to continue doing things once they stopped being comfortable for me. I think the benefits of suffering are considerably overrated, and the benefits of self-care and actively valuing one's own happiness are considerably underrated.

As for being well-off, at times this philosophy has led me to quit jobs with no other job on the horizon, live off my credit cards, and wonder where the rent money would come from. I still have no regrets whatsoever.

All of that being said: I certainly don't mock people who do things the goal-driven way, since it seems to work for them. And I think a great many people are not at all cut out to take the entrepreneurial approach and will do much better with some external direction. I just don't think the iterative, reevaluative process should be scorned as unworkable.