In addition, one other paper trail that might illumine Kagan's intellectual development awaits anyone willing to head up to Princeton to examine the archives of the The Daily Princetonian, where Kagan served as Editorial Chairman (some years before I held the same post). Here is one article from the Prince that suggests that careful perusal of those records might be of interest to any journalist located in the northeast with a curious turn of mind (online archives begin only in 1998, but there are bound copies of the Prince from many, many years gone by).
Did Elena Kagan have a weekly column in the paper? That might be of interest -- as would the "staff editorials" frequently penned by the editorial chairman (as part of a collaborative effort with the rest of the paper's leadership team).
Obviously, people's thinking evolves over time, and obtaining the more recent records of Kagan's White House tenure is more important. But earlier writings might help us understand why someone as far left as Barack Obama is willing to take a chance on a nominee like Kagan, who has had so little to say, publicly, about her views -- at least in recent years. At the very least, they might help Americans come to an informed decision about whether Kagan's thesis (about the history of socialism) was part of an integrated political commitment, or just an intellectual interest (as her thesis adviser insists in the linked article).