This theory (also freud, IMO) demonstrates that ideas can have value regardless of being true or false. Just considering such ideas opens the mind to others. The interest so many great science and science fiction authors took in this theory is, IMO, proof.
There are some interestingly elements that are interestingly parsimonious with YNH's take on human history in 'Sapiens.' YNH places a lot of emphasis on what he calls "fictions," which overlaps a lot with Jaynes' "metaphor." Also in common, is the notion that cultural memes, rather than biological genes are responsible for our humanity.
The inner monologue, no doubt, deserves all the pondering it gets.