Sonic varnishes would be cool, some sort of jelly that causes resonance on an impact being the explanation. That said, it's been stated a lot that the crafting system is a monster to work with, so I'd be pretty surprised if there was any interest in adding more to an existing craft.
Positive varnishes wouldn't heal on hit unless you scripted them to, because positive damage doesn't heal the living in NWN, it just hurts them. I'm not sure we need a craftable AoE heal, but it'd probably be easier to just add a craftable alchemical item like a quintessence that had uses of Circle of Healing. As a damage varnish, too imbalancing imo.