I would agree and argue that all of the inter-chapter text serves to enhance the story and, in fact, operates as an intergral part of it.  Watchmen is not one narrative, but a series of conjoined stories that only come together as the finished product when read and grouped together.   The main sections of the comic are much poorer for the lack of supporting material; some would call it pace-breaking exposition, but in the long run, how much of a pace does the comic really have?

“Under the Hood” cements the point of deviation from the original timeline (what we’d call “the real world”), and adds what seems to be a voice of sanity in the midst of a collapsing world.  It is part of Moore’s critique of comics and their characters, and probably the origin of the now-famous “no capes” trope, regarding Mason’s attitude towards Dollar Bill’s costume-driven demise, the victim of a marketing ploy.  Comic companies strive for success in the same ways, sacrificing character development, story, and quality artwork for reader enticements (“This issue, someone DIES!!!  Or maybe they come back to life.  We’re really not sure anymore.  Please buy it anyways!”).