Ancillary themes of UFOs and gluttony in the movie "The Man Who Wasn't There"

There seems to be some themes about gluttony in the movie. The lawyer eating a lot and the other barber. Just typical gluttony commentary or what?

Also, what's up with the UFOs? Just thrown in to lend m ore mysterious atmosphere or do they have a large purpose to the movie?

Is there a puzzle that can be solved with the movie or is it just meant to be about alienation and noir?