Complex sentence: Skilled spies of enemy races are essential to a well-conducted espionage program, and the player can bolster his or her forces by grabbing a skilled fighter, or give oneself factories/mines/towers of science a boost by hiring a highly skilled professional.
Split into simpler sentences: Skilled spies of enemy races are essential to a well-conducted espionage program. And occasionally you might just like to bolster your forces by grabbing a skilled fighter, or give you factories/mines/towers of science a boost by hiring a highly skilled professional.