This is another guest post from @iGrrrl, a grant writing consultant.
A few comments I've seen around, on top of my experience working with applicants for K-flavored and other career development grants, make it clear that they think the required career development parts are just window dressing. I hear complaints that they have to write a mentoring plan, and then they never do anything that is on it.
Is it the mentor's fault? The people who signed letters to be on the mentoring committee? No. (I'm going to switch voice now and talk at you K99/R00 or other K and F applicants/awardees.) And whose fault is it?
The fault is YOURS. No one cares about your career as much as you do, and even if it went in as fiction on paper, it is YOUR responsibility to make it reality. Otherwise you'll never know if it would have made a difference to tap into the brains on your mentoring committee, to impress them with your initiative and willingness to learn. Making someone feel smart and important to you (while also getting good advice) is a good way to increase their sponsorship of you--inviting you present at meetings, to small subdisciplinary meetings, talking positively about you.
I think it's easy for young people to underestimate the impact of the positive regard of more senior faculty, or for you young folks to know how that plays out in reality. No, they're not gossiping about you; they have better things to do. But that 'dream team' remembers that they signed letters for you and then never heard from you again.