Enhance ability has 6 variants for each ability score. Yes, you can cast in dialogue too. However, it lasts all day until concentration is dropped.
I use it in the druids' grove and helps me blast through most dialogues. A fair Cha14 helps, as does Guidance - make sure you don't choose same spellcaster for Enhance ability, or you'll lose the first one cast.
Bardic spellcasting grants a 1st level spell and 2x cantrips. Performer feat gives +1 Cha and musical instruments. It so happens that you get a feat for every 4 class levels, so Wiz12 has 3x feats, compared to Wiz11/Bard1 having only 2. That means the single classed can afford soft multiclassing feats better, which makes its own sense.
I did a run where Gale prepared Detect thoughts plus I had some extra scrolls handy. He could get through a lot of dialogues. Didn't test Fox's cunning, but that should work and if so, an Int character can blast through too.
Oh yeah, did that too with paladin MC with headband of intellect. With Gale preparing Detect thoughts, got best of both worlds. Problem was I had to remember to switch back to helmet for fights. Often forgot and took unnecessary critical hits.
In that same run, I picked carefully who was leading the party whenever we approached NPCs. Didn't have many issues with wrong companions talking, except for the odd surprise dialogue or ones where MC is scripted to talk.
