Disclaimer: My character is a 20 El/Mo in the Crystal Desert with relatively limited PvP experience.
I used Aura, like most low-level characters, in the first 8 levels or so, until it got scooted off of my skill bar for more useful things.
However, I've recently had two experiences that have somewhat changed my mind.
1) I played a protection monk that was highly effective until my enchantments started getting dropped, and I kept getting killed by break enchantment on my healing breezes
2) I got Ether Renewal and started playing around with it.
With no added skills, and assuming 350% regen, Aura gives you nearly 5 health per second, or 2 and a half pips of regen, for the cost of 10 energy per 60 seconds (the equivalent of half an arrow of mana degen) and a slot on your skill bar. You also can pay that 10 energy whenever you feel like it; you can cast it before the gate opens in PvP and regenerate the energy, for instance.
You also wind up getting the healing when you need it: usually you need healing the most when you're spamming spells the fastest.
Concerning the two points up above:
1) Enchantment removal is a real pain in the rear. Many builds rely on enchantments: attunements, armor of earth, and whatever the party monk may be throwing your way. The more "buffer" enchantments you have in your effects list ahead of the ones that really matter (armor of earth), the less likely you are to get what you really need stripped.
2) Aura synergises with Ether Renewal in three ways.
First, it gives you more kickback from ER since you have more enchantments active.
Second, it gives you more benefit since under Ether Renewal you're casting more spells. Assume that you have Aura, an Attunement, and Ether Renewal active; then any spell you cast gives you 12 energy back, which when used for spells will give you 42 life. By letting you burn through energy faster, ER lets you get more benefit from Aura.
Third, it is itself a very quick-cast spell. Often under ER you're trying to spam spells as quickly as possible to get the benefits. It casts in a second total (counting aftercast), giving you a net +2 energy and +15 life, and giving you 35 more life if you already have it active. When you're out of other spells to cast, renewing Aura while under ER can be a beneficial thing to do. Plus, if Aura has dropped, it'll appear after ER on your skill bar, insulating you from removal.
The drawback to including Aura, of course, is the use of a skill slot. This means that it's no good in convoluted builds that require lots of skills. It also means that you'll have fewer attack spells to spam while ER is active, so you can find yourself waiting on skills to recharge and will have to stop casting. As mentioned above you can always just cast Aura in that situation, but wouldn't you rather throw another attack spell?
The ideal skillset to use Aura and ER, then, has an attack skill set that is (naturally) more energy-limited than cast-rate or recharge-limited (skills like Stoning and Flame Burst). You want to be able to spam spells constantly while under ER, and you'll have the energy to do it.
Is Aura useful in an Ether Renewal build? Seems like by using the huge mana boost from ER in conjunction with other enchantments (an attunement, aura, itself, and maybe an armor) you can cast high-energy spells rather quickly and, by doing so, get a significant boost of life. Aura will also let you protect those other enchantments, in the case of a build that relies on those other enchantments to survive. Losing Aura won't kill you like losing Armor of Earth, and it's quick to recast.
(I am, by my own admission, relatively new at this game. Please don't tell me I'm wrong without explaining why.)
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