I mostly meant that suggestion as a joke, but to be real I can't imagine reading so many books that you run out of room for enough bookshelves. I have several boxes of books and it's a huge pain when moving to a new apartment, but otherwise I just get more shelves when I need more. I don't think having a lot of full bookshelves would ever be perceived by others as a hoarder scenario if the apartment is kept clean and neat. But I do think that being seen to own many books will generally give people a better impression of you, so I was sort of serious with that joke.