The fiction piece in this week's New Yorker deals with some of the same themes as Eliezer's "Three Worlds Collide"; viz., the clash of value systems (and the difficulty of seeing those with a different value system as rational), and the idea of humanity developing in ways that seem bizarre/grotesque/evil to us.
Not if it's so rapid you don't have time to properly enjoy it, or put another way if it's so rapid it clips the top of your progress-detector and all progress above that is simply wasted in terms of your hedonic enjoyment.
I am skeptical of the idea that the smallest of children have the conceptual sophistication to notice and enjoy their growth and improvement. Older children may, but then - adults can improve and grow too, while being competent and productive (and, at least potentially, self-conscious of the growth) all the while. However, my individual perspective is probably uncommon here: I didn't like anything about being a child that has turned out to be unique to childhood.