concentrate the effect on the source of the aura. e.g. insead of sona-w giving everyone in range a 200hp shield give sona a 500hp(or whatever is balanced of course) shield that gets depleted first when allies in range take damage. combine with some clear visuals for what is happening and BAM: aura like effect that is easy to appreciate. here you go riot, i fixed another one of your problems, youre welcome. too bad ill be ignored again.
Sona does not have auras, her abilities are single charge buffs.
and if you want sonas e to not feel trashy switch from ms to another effect, ms is too strong a stat to buff to a noticable level and its also something continuous, which again makes it harded to be noticed. make it something unique where you can add a clear visual cue upon use, like 0.1xlvl seconds off of ability cooldowns when casting in range. (an ability going on cd is a clearly separated moment instead of the continous ms thing.) of course thats just an example but in general some unique utility would give her a clear role and "why am i picking sona" thing.
You bring up an interesting design idea. But it would probably require some significant changes to her heal to be workable or the ability would become overloaded.
