I never made it all the way through Dune but my sister loved the series. She did have a copy of the Dune Encyclopedia (written with Frank Herbert's approval but later disowned by his estate). I did enjoy reading the encyclopedia because I could read about the characters in the books. I remember marveling at the scientific and cultural knowledge it took to generate these fictional worlds and peoples. Same reason I liked reading about Tolkein and about CS Lewis or about Hitchcock or was obsessed with 'making of' books for different movies. I'm obsessed with process.
The Dune Encyclopedia