Exothermic aura wouldn't be a use-every-combat sort of ability. It would let you stop being on fire (if you're an ambush build, you probably aren't wearing an antithermic armor suit) if something makes you catch fire, and it would provide several useful opportunities, like kiting Industrial Bots and letting them waste their flamethrower on you, or making a lake of fire to dissuade stealthed Crawlers from coming up and saying hello (they tend to wait, stealthed, at the edge of the fire, giving you time to see them and deal with them).
From a strictly lore standpoint, Persuasion isn't much help. It does have impact on the game world, but for lore, I don't think it gives you anything you can't get via other means. If you really want to maximize your ability to get game lore, you need to find four more points for Will (or go read the compilation of Mysterious Pillar text).
