I like those sorts of vocal tics when they are part of how the dialogue is spoken, but not when they're made outside the scope of the words used.

Yeah, that's well-stated, and I think it's where I stand on those, too. I want the sentence to have a yawn or sigh or laugh in the words, rather than to pause for the sound effect and then have the words separately.

That's a good point, too, that a reader can amp up the narration to match the speech in intense moments, rather than just toning down the speech. That wouldn't have worked in this one, because the tone change caught the POV character by surprise, but it does work in a lot of readings, and I like it when the reader makes that choice. I can think of one reader who doesn't seem to do that with the narration, and it made for somewhat abrupt-feeling sex scenes, switching back and forth between calm narration and super-turned-on dialogue.