And though this mix obviously came to me when thinking about Gatsby, we could expand it to the wider genre of Roaring Twenties/Gilded Age fiction: anything where we have rich people going around, ignoring or exploiting the poor or trying desperately to escape the ranks of the poor.
You might argue that vampires are the perfect monster to talk about the rich, which, well, you're not wrong about. With compound interest and some safe investing, most long-lived vampires should be rich. But Great Gatsby isn't about rich people only: it's about people who may (or may not) be rich who are very insecure about their status.
Which is why I think werewolves are the perfect monster-metaphor to explore this issue. Also, wouldn't it be amazing to see a werewolf rampage through some decadent 1920s speakeasy? Imagine what Baz Luhrmann's Great Gatsby would be like with werewolves.
Why aren't you writing werewolf Gatsby?