The great thing about Gödel, Escher, Bach is how readable it is in spite of its subject matter. (I've read it closely twice, and still dip into it to look around a familiar neighborhood years later.) Dickins, I have read, and he's quite easy to, but I've never much cared for his stories. I can always hear the wordometer clicking over on every other page, as it seemed he really wrote for money and not for joy. Don Quixote, like a lot of pre-18th century literature is tough-going in patches, but it's rather pleasant read. And good for your grandfather; more children should be given good books to read rather than the trash that's usually foisted on them.