That sort of thing - 5000ish pages of plain text - is exactly what they invented e-readers for.

There are factors working against second-hand book retailing that are much more significant than charity shops:

- the abolition of the Net Book Agreement meant that the cheapest books could be sold REALLY cheap by retailers who could move them in truckloads - Tesco in particular. Charity shops now find it hard to get customers for cheap clothes, given how cheap Primark is: Tesco are the Primark of bookselling.

- electronic distribution has eaten into sales of the same cheap stuff. Second hand hardcopy romance is only saleable as pulp.

- at the high end, just about everybody with a first edition of "1984" now knows they can sell it themselves on EBay and get more for it than a second-hand dealer will offer. So the high end has gone too (and second-hand dealers can't moan about that in public as they can about Oxfam, since it might give people ideas)