Rebecca Giblin has self-archived "What Happens When Books Enter the Public Domain? Testing Copyright's Underuse Hypothesis Across Australia, New Zealand, the United States and Canada" in SSRN.
Here's an excerpt:
We find that books are actually less available where they are under copyright than where they are in the public domain, and that commercial publishers seem undeterred from investing in works even where others are competing to supply the same titles. We also find that exclusive rights do not appear to trigger investment in works that have low commercial demand, with books from 59% of the 'culturally valuable' authors we sampled unavailable in any jurisdiction, regardless of copyright status.
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