Hello,
What if every specialist skill could be improved through experience? Say, every time you search for a coal deposit, your specialist gets a certain amount of experience in all coal search-related skills. This could supplement the science system, with books used to unlock the ability to develop a certain skill greater, and of course, for unlocking new skills as you go further up the science tree. This would further reward specialist diversification, and add some depth to an otherwise simple system.
TL;DR: make using specialists make them better.