I went back to my newer, less-glitched save to start playing the game properly again, and the journal clearing seems to be helping in that one, too. I noticed yesterday when I loaded - about eight hours in - that Haven's sound was a bit glitchy (no music, sometimes footsteps cutting out), so I cleaned out the journal whilst there, and immediately got music.I went to the Storm Coast to pick up Bull, and heard Viv/Sera banter for the first time across both games. (Again, went six hours plus with no music/banter whatsoever at the Coast in my first game.) When I took the three of them to the Hinterlands, I heard 2x Bull/Viv. (Seriously, in the other 40hr+ in the other game, and Viv would not talk, no matter what!) Music and combat soundsets have been there 100% of the time. Never realised how noisy Bull was, actually. Lots of yelling. I don't know how much banter I'm getting comparatively, but it's way too exciting than it should be to hear Viv talk.
The difference I can think of between the two playthroughs, is that the first time around I spent 3hrs+ at Haven talking to people (it would have filled up the codex), and the second time around, I only went to the blacksmith etc, before jumping into the Hinterlands. I had sound issues from the get go in the Hinterlands the first time around - extremely rare music, banter, hours of silence, etc. The only difference I can think of is that the codex would have been filling up by the time I got to the Hinterlands, and then I would have started doing a ton of quests on top of all that, so what sound that was working quickly stopped. With the newer save, there wasn't much in the codex by the time I got there, so the sound was working perfectly without having to use any tricks, as far as I could see. It may be a coincidence with a dash of the placebo effect, but really, that is the only difference that I had a direct influence on between my two saves.
I've also been trying to behave myself and leave the world map properly, which sometimes isn't easy with a lot of distance to cover before the exit! I've been trying to keep pinging and fast travel to a bare minimum. No idea if it helps, though, and might not be able to keep it up forever. No one expects the Pingquisition, sigh. I guess every time I go to Haven, I'll clear out the journal, hope it keeps helping.
I'm still baffled why some people wouldn't be having any issues with this, and why some people would. Why wouldn't the journal be doing it to everyone? I saw Shinobi on NeoGAF mention the other day that the poor devs were finding the banter bug to be 'a pain in the ass', so I don't envy the devs trying to figure it out.