Well, we should probably widen it to cover the Coens in general since a lot of similar imagery shows up in other films. Raising Arizona has the biker bounty hunter who certainly seems far removed from reality, though the film itelf is taken on the narrative level to be literate.
And of course that is something to keep in mind. There is the metaphorical within the diegetic world, ie things being shown aren't really happening, and then there is the bizarre narrative in which the diegetic is real but the characters and actions are meant to be highly metaphorical.
Think of Gulliver's Travels for example, or Frankenstein, or especially many German children's fables like Hansel and Gretel, etc. Such stories package social commentary WITHIN the narrative, but the narrative itself still "exists" in as much as the story is really happening as it is presented.
I consider that different than a film like Fight Club.
Alice in Wonderland and Wizard of Oz sort of bridge the gap. It is all a dream but for the most part the narrative is meant to be taken as it is, actions really are occuring while the social commentary is buried as allegory, and not all that deeply in Wonderland.
So when I read Fink as literate that doesn't disallow for bizarre actions nor for symbolism. It just means that the symbolic characters don't have to be symbolic to other characters WITHIN the film (Goodman as Fink's conscious/vengence/whatever) since they can simply be symbolic to the audience (Goodman as the representation of the common man fitting with the overall allegory being presented).
And all of that doesn't mean that I dismiss your viewpoint, Vince. You make a lot of sense. I just don't think that some of the actions inherently mean that its all in Barton's head, or is to some extent. Maybe they are, or maybe the Coens just have a penchant for certain symbolism that keeps popping up in their films as character types, character interaction, and action within the film.
Dickens used real stories and packaged his commentary on the industrial revolution by having the same types of oppressed characters put upon by the same types of bureaucracy, industry, and corrupt dictator characters. Scrooge is really visited by ghosts but at the same time Dickens is commenting on the false promise of industry and how it would bring about eventual ruin in the future (ie, Scrooge sees his own death).