Al Brophy has a working paper "The Relationship Between Law Review Citations and Law School Rankings" at SSRN. Brophy has posted a blog entry about his paper at http://www.concurringopinions.com/archives/2005/12/law_review_cita_1.html.
His chief finding is a high correlation between first-tier law schools and citations to their journals, and progressively lower correlations for law schools in the 2nd, 3rd, or 4th-tier. Brophy suggests that "law reviews are schools' ambassadors to the rest of the legal academy. Much of what people at other schools know about a school's academic orientation may come from the articles and notes published in the school's law journals. Thus, those schools seeking to advance in reputation may want to pay attention to their law reviews." One interesting suggestion offered by Brophy is that reputational assessments of 3rd and 4th-tier law schools as recorded by U.S. News may simply be inaccurate, and that the more objective measurement of citations to the law reviews of those schools could be used to correct for peer-assessment fuzziness.
It does seem likely that manipulation of law school journal rankings is an (as yet) under-explored component of the ongoing effort by law schools to influence their position in the U.S. News rankings.