Thing is, if we keep c/r him, he's either going to stop cbetting, or stop folding to the c/r. If we're quick to see he has adjusted, then we can counter-adjust.

If we think villain stops betting with marginal or missed hands after his flop cbet, I like to c/r this flop because it might encourage a spewy adjustment in later hands from this villain, no-one likes being pushed around. Just avoid the temptation to keep firing if we c/r him with air and he continues, because then he's exploiting us.

To answer your question of how often we should exploit these villains... we do it as often as we think we can get away with it! We exploit until they adjust.