Imho, Mike gives a good answer. If one must choose, begin with broad, diagnostic knowledge (fox knows many things), and continue to specialize (hedgehog knows but one).
If one is in it for rewards, such as money, the specialist makes more. However, if the specialty is not in demand, e.g. ethnic studies, then the market value is primarily for instructors of same to students, not otherwise in the market.
If the specialty is not in demand, and the philosopher is ahead of her time re presenting answers to developing problems, then as a voice crying in the wilderness, e.g. a van Gogh.