Should untenured faculty write in multiple areas, or concentrate on just one?

There's an interesting discusssion here, though I'm inclined to think (as some commenters suggest) that what matters is writing, not the area(s).  On the other hand, I've certainly been party to tenure decisions where the faculty discusses whether the candidate will be a "leader" in his or her field, and to the extent a school values that, that may favor more focussed scholarship.