I love Mazes and Monsters. It was hilariously stupid. I still play D&D every weekend, same campaign been running since I was 14. M&M was just a horrible, hilarious bit of utter nonsense.
I have to agree that any Anne Rice would be completely riffable. Her writing is laughably awful, surviving only due to the extreme pandering to daffy way-too-serious goths. A lot of Stephen King is very riffable, I'd say most notably The Tommyknockers. It's like issues upon issues upon issues. So many issues this man has.
Robert Sawyer, there's a damn goon if there ever was one. That heavy handed babbling ninnyhammer. Seen subtler politicizing and condemnation of various bits and bobs from an anarchist metal band. Also, he looks really weird to me. I know that's not very adult, but, come on. Have you ever seen him? He always looks sort of drunk and weird to me, with a kind of monkey-face expression, and his glasses pushed up way too far on his face.
Also, I love the Divine Comedy, but it'd be totally riffable. Well, at least Hell, and probably Purgatory. Paradise gets a bit weighty, though I'm sure it could be made fun of too, it's just, it's not so funny inherently as the layers of Hell with their really bizarre torture and all.