@pdurrant is spot-on in stating that eBooks have significant restrictions on their use (assuming DRM). This, for me, is the dividing line in determining the value of each book
for my use, not necessarily reflective of the market in general.
Books are expensive if you buy first-edition hardbacks, perhaps $30US. They are somewhat less so with first run paperbacks, typically $15US. Later runs come in around $10US and sometimes a bit lower, so for $10US I can choose an eBook from a major author or wait a year or two for a $10US pBook, or go find one for 'free' in my local library. The question then is, would I want to keep it, loan it to other book-loving friends, or give it away and/or delete/archive it. What value do I place on the ability to loan it to a friend? If it's an "airport" book that's just a fun read with little redeeming psychological or informational value, it's worth less to me than a classic or a literary gem. Fun books are a weekend fling - a cheap mistress perhaps - but nothing of perpetual interest. (Apologies for the sexual bias in that analogy.
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So my answer is, "it depends on the book." I return to a few books to re-read certain passages, seldom the entire book. In recent years, I have collected statements or paragraphs of choice in a text file for future retrieval and consideration. My bookshelves have been purged of excess volumes and donated to local libraries or given to appreciative friends, but my eBooks never will be. That restriction is "value added" to publishers and authors and is a major consideration as to which format I choose for each book and what I'm willing to pay for it. pBooks should generate more sales and hence more profit due to their lack of 'unauthorized' circulation potential. Yes, I know how to remove DRM restrictions from books, but I don't go there. If I want to share a book or if I purchase a book to share, I buy a pBook if the price is reasonable. That ability to share has a value all its own and may well be the reason pBooks will survive and continue to demand slightly higher prices.