China Miéville has one or two interesting things to say in a recent interview, including this:
I spend a lot of time arguing for literalism of fantastic, rather than its reduction to allegory. Metaphor is inevitable but it escapes our intent, so we should relax about it. Our monsters are about themselves, and they can get on with being about all sorts of other stuff too, but if we want them to be primarily that, and don’t enjoy their monstrousness, they’re dead and nothing. [...] it’s what Toby Litt brilliantly called the “Scooby Doo Impasse”—that people always already know that they’ll pull the mask off the monster and see what it “really” is/means. The notion that that is what makes it legitimate is a very drab kind of heavy-handedness. [...] plenty of monsters get hobbled by their “meaning”. The Coppola Bram Stoker’s Dracula vampire had to shuffle along, so weighed down was he by bloated historical import. None of this is to say that monsters don’t mean things other than themselves—of course they do—but that to me they do so best when they believe in themselves.
This distinction between the more or less heavy-handed monster-as-metaphor and the monster as a thing in itself (and let's not wander into the semiotics mire) is a somewhat different, but related distinction to one that I first heard from, I think, Philotomy. "Story" and naturalism be damned—the boggles are just there, lurking quietly in that dark room, waiting for an unwary adventurer to open the door.