[osric]

the single aura is a "bonus buff" in my opinion. you have the castable buffs, and then an aura you can use. you select your aura depending on what you role in the group is going to be. if you'll be up with the melee guys damaging enemies you'll want some kind of melee aura, be it increased damage, reduced damage taken, etc etc. if you're going to be back healing and standing near the mages/rangers you'll want something that increases magic damage, lowers mana use, increases mana regen, spell crit chance, etc etc.

i don't see it as limiting, i see it as giving you just one more versatile way to buff close-by party members.