The question of how often to reread versus how often to read new things is one I've settled for myself but not in a way that generalizes. My current practice is roughly one reread for every five new books. The rereads are of books I think I misread the first time, or books I think will have changed because I've changed.

The argument for rereading is that it compounds. Each time you return to a book you know, you're reading it with the accretion of everything you've read since. The argument against is that there are too many books and rereading is opportunity cost.

I think the opportunity cost framing is wrong. Reading is not efficiently consuming content. It's developing a relationship with literature over time. Rereading is part of that relationship, not a diversion from it.