Prof. Lucian Bebchuk of the Harvard Law School authored a study that analyzes the stock market reactions to both the Delaware Chancery Court ruling in Airgas that, he argues, weakened the anti-takeover force of staggered boards, and the Delaware Supreme Court Airgas ruling that overturned it.

He provides the following overview to the analysis:

We find that the first ruling benefitted shareholders of affected companies and that the second ruling eliminated these gains. Our consistent findings over the two events enable us to confirm with high level of confidence that market participants place a positive value on weakening the anti-takeover force of staggered boards and that shareholders would do well to continue pressing for board declassification and that the ongoing process of board declassification is likely to benefit shareholders. 

The study is available here. Prof. Larry Ribstein comments on the study and its analysis here.