I'm curious why you chose to put Twain and Vonnegut in there. My take on their writings is that they were amazing storytellers. Twain used simple language and local color to produce wonderful imagery with an expertise that few achieved before him. He whisks us away and drops us into a place in history that we otherwise never could have experienced.
Vonnegut lets us in on the insane parts of his mind. He tells interesting stories and frames them in a way that I, personally, never would. Even if I had some of his crazy ideas, I wouldn't think about them at all like he does. I've never seen another author break down the fourth wall the way Vonnegut did; after reading a few of his books, I felt like I understood a lot about the way he thought. (Another author who did this was Douglas Adams, whose output was markedly less than Vonnegut's, and Adams wasn't quite as "out there" as Vonnegut.)
In other words, I've never really heard of reading Twain and Vonnegut for their ideas or philosophies. While I would argue that their beliefs were rather anomalous for their times, I wouldn't consider their philosophies to be the main virtues of their writings.
Vonnegut lets us in on the insane parts of his mind. He tells interesting stories and frames them in a way that I, personally, never would. Even if I had some of his crazy ideas, I wouldn't think about them at all like he does. I've never seen another author break down the fourth wall the way Vonnegut did; after reading a few of his books, I felt like I understood a lot about the way he thought. (Another author who did this was Douglas Adams, whose output was markedly less than Vonnegut's, and Adams wasn't quite as "out there" as Vonnegut.)
In other words, I've never really heard of reading Twain and Vonnegut for their ideas or philosophies. While I would argue that their beliefs were rather anomalous for their times, I wouldn't consider their philosophies to be the main virtues of their writings.