My attention was drawn to an article by an author about having being solicited to sell his papers (past and future) to a university archive and his musings about the relationship this bears to his existing and future literary reputation, the impact of the prospect of the preservation of his correspondence on his self-expression, etc.
Maybe it's because I'm a historian rather than a literary scholar, or maybe because I'm an archivist, but it's not necessarily the intrinsic value of the work of the individual that makes the papers interesting. It may be what people wrote to them, their circles and connections, what their papers tell us about relatively quotidien details of their life. Sometimes the papers of a relatively minor figure who was well-networked, or who kept scrapbooks or diaries, can be more informative than those of a major figure who didn't bother to keep things.
It's only relatively recently that most people routinely have a copy of outgoing correspondence, because they've saved the word-processed file of the letter, or because it all happens in email anyway. Certainly from at least the early twentieth century one does find some individuals (as well as people who needed to keep copies for business purposes) making carbons of their letters out, but on the whole this remained fairly rare. In the past a letter was despatched to its recipient, to be preserved, torn up, burnt, have shopping lists written on the back, etc and its survival as a record of the sender's thoughts and emotions a haphazard matter.
Embarrassing or revelatory letters or bundles of correspondence still do occasionally turn up.
A further thought about archives in general that was my takeaway from a fascinating workshop discussion on Women and Gender in the Archives at the Berkshire Women's History conference: the great extent to which discussion of archives of [x] all tend to end up with the same issues and problems common to all archives (which are not those of central government) - whether papers, of individuals or organisations, have been kept at all, if they have, how complete are they or has expurgation/damage occurred, the under-resourcing of archives, the importance (and the limitations) of cataloguing and provision of metadata, the digitisation question, the continuing fascination and importance of handling the originals, etc etc.