If you're not on, you're not creating runs, and for those who are hitting 1-2, you need to be on, so that your 3-4-5 guys (usually your best run producers) can send you home.
I like Crawford, I'd like to see his OBP to get up, and for him to start racking up the hits again. However, Pedroia is on base at a much higher rate, which equals to more opportunities for runs, whether he's fast or not does not matter when the OBP differential is that significant.