I don't think there's a set answer as to how much detail is necessary within a persona. The development teams and Business Analysts I'm used to working with deals with persona as the basis of the overarching "saga" levels that directly influences epic level work. Because once you go down into individual stories, it's been boiled down to simple one-liner task. You really don't get anything more than "As [Persona X] I need [abc] so that I can do [xyz]." Which really doesn't tell you much about the persona at all.
The Persona acts as your placeholder for a typical user within a user group. So the fuzz rule of thumb I use is I need enough details to be able to imagine the persona as a real person so that when I read an epic level scenario, I know enough background to know: what the person wants, why they want to do it, how would they prefer to do things, what's on their mind before, during and after they've done this thing. Having some info about demographic/personality is helpful in extrapolating for non-happy path flows and determining priority of items for the dev team.