I don't understand the value in this. It's some mundane letters somebody wrote to his mother about his daily activities? Is there a subtle meaning in there?

It's A) creepy voyeurism disguised as interest in the life of a creative person and B) the eight billionth reminder to destroy anything you wouldn't want published some day.

If you've ever read and enjoyed his creative writing, I think you'd likely find the letters interesting

If that's still hard to understand, haven't you ever wondered about the personality of someone who created something you thought interesting?