IMO auras at this point are: Unholy, tich meh
Devotion, trueshot
Thorns
Everything else
Vampiric aura
Negative auras other than tich meh.
Of these I think that Vampiric and frost would be easiest to buff in a meaningful way.
Vampiric, at L5 and L6 make it have 50% of its effect on ranged units, vampiric itself isn't bad, it's just the fact that an item completely shines it out of its slot that makes it not worth the slot in the least bit.
Frost aura I think should have a massive effect on move speed, have it be the anti unholy, if not a little stronger. Even at L6 this ability isn't scary in my opinion.