[Quoth]

Aside from junk or not, the Big Five are poorer at picking winners than experts on horses at the races, if you go by percentage of books making advance in royalties (though those can make a profit). Also why only text books as POD? Surely nothing should be out of print now?

Profitable Junk: Hyped on media giving great sales, but vast qty in local charity shops that look pristine.
Unprofitable: Gets pulped, maybe without reviews. Might be a great book but they don't bother even with an ebook, so we will never know.
Snob literature: Very famous and highly regarded but only a small percentage of readers complete the book.

Traditionally a book snob bought a library of books and didn't read any of them. Maybe there is a better term.

Then there are people that invest / collect books, but don't read, like some so called fine Art collectors (I can hear my daughter shouting buy from living artists). Buying anything purely as a speculative investment isn't appreciation. It's knowing the price and not the value.