A couple experts have even surmised that mid-life crises may be partly the result of development of the Inferior and a desire to explore and restructure one's life in accordance with the new function.
As for whether we should deliberately develop our non-Dominant functions, it seems like the some of the older experts frown on it--they indicate that premature exposure to the non-Dominant functions will be too scary for most people and smacks of pushing "type falsification" on people.
On the other hand, some of the newer experts and books are taking the opposite tack and encouraging people to play around with the non-Dominant functions, saying that as long as people have a good grasp of how functions work they can explore their non-Dominant functions as a creative or self-development exercise. BestFitType.com is kind of a clearing house on anything to do with functions, and it's pushing a book on that very subject:
Also, I ran across a couple articles elsewhere describing how recognition and exploration of non-Dominant functions (and specifically the Inferior) is being looked at as a therapy tool for people as young as college age to help them deal with anxiety and stress issues.The activities included in this book were compiled so you can consciously and purposefully increase your ability to appropriately use the skills that are associated with each of the eight Jungian functions. As you perform any one of these activities, first assess how comfortable you are with the skill set, then learn how to incorporate the skills into your behaviors.
So clearly there is a wide range of thinking on the subject.
I'm not pushing anyone to do anything they don't want to do. But a lot of members of this board are at or close to their 30s. Might as well be aware of what's coming. Clinging to one's Dominant function just because "That's who I am!" isn't very realistic. As we get older, we take on more responsibilities and need to be more adaptable. It's increasingly looking like development of one's non-Dominant functions is a natural part of the aging process anyway, whether we like it or not.