I did my Masters degree before gravitating toward law school, but I'm so grateful for having completed the MA first. My graduate work taught me how to think analytically, and it taught me how to write scholarly, journal-quality pepers. After composing several forty-page analyses, as well as a two-hundred-page thesis, I feel far more prepared for the rigors of law school than many of my friends did when they entered.
I'm not saying that a graduate degree will make you a successful law student, or even get you into a good school. But given the right circumstances, a graduate education can strengthen the skills you'll need as a law student.