Something tells me one of you is speaking about fiction and one of you is speaking about nonfiction.

Inflection, emotion, tone, character-specific affects and all that can really change the audiobook experience for fiction. Your mentioning of footnote references and GNU suggests you're talking about nonfiction, perhaps technical books. For that, a voice that never significantly changes is fine and maybe even a good thing. For fiction it'd be a big step down from a professional human reader who understands the story and the characters' mental states.