"There is no greater joy in life than typing a sentence, realising it needs a clarification, a caveat, an addendum (in the same sentence, not a new one) and, guess what, parentheses are right there for you."

That's what I'd do. Note the conversion of the first comma to "and," as well.

I find m-dashes easier to read for most other purposes. They’re nicer in longer asides because they’re a little more visually prominent, while also (for some reason) not breaking my mental flow quite so much. They’re far nicer looking when an aside comes at the end of a sentence, as you don’t need to close an m-dash. That always looks like crap with parenthesis, as if the author should have thought of a way to avoid doing that, while with the m-dash there’s no problem at all.

(Unrelated: The alt-code for em-dash on Windows is Alt+0151. I just typed my first manual em-dash wow exciting.)

I definitely prefer it un-spaced, though, personally.

> And also occasionally — occasionally — one just needs a random dramatic pause.

> And also occasionally (occasionally) one just needs a random dramatic pause.

I know which one I'd rather read. Though, frankly, I'd prefer neither and I'm trying to remove this kind of thing from my own writing.

In a first example, the second "occasionally" is stressed, when in second example it feels almost whispered.

But what I see from trawling the posts made by narrators, a lot of them do mention that em-dashes are read as interruptions with sudden tonal shift, while cursive implies a non-interuptive tonal shift.

That said, apparently, most audiobook authors actually supplement their own guidance on how to read their books. I haven't found any universal guide yet.