It's not like the prof is going to attach their CV to the rec... right?
It might (MIGHT) make a difference for grad school in whatever field the person is in, but I doubt it would for law school. I got one of my recs from a grad student and it didn't seem to hurt me. I feel like recs probably only really matter if you're on the border between in and out, or if it's really terrible. And if you're on the border, like others have said, better to get one from someone who knows you and will say nice, personal things about you than something like:
xynder earned an A in my course on Widget Theory. xynder has been heavily involved in [regurgitate resume here] while in school. Please consider xynder for admission.
John Doe, Ph.D.
Oh, Dr. Doe edits a journal? He's an expert in applied something-or-other? Big deal... I still don't know anything about this student that I didn't know before I wasted 5 minutes reading this letter!