Many good things are already said.
If you want to make auras become relevant for constructed or tournamental play, you have to change things even more than you do by now.
There are auras like
Spreading Seas 
or
Eldrazi Conscription 
that are used in some decks.
The first one deals with the problem in an easy way... card disadvantage is negated by drawing a card. The second one didn't negate the disadvantage, but in combination with
Sovereigns of Lost Alara 
it is a "have an instantaneous answer or die".
But what do both cards have in common? (beside being an aura...)
They fight around the "instantaneous answer" problem!
Let's assume, there would be more cards that allow you to give a land shroud until the end of the turn. Then, Spreading Seas would be as useless as any other creature-aura. Even the draw effect doesn't happen. Therefore the "draw 1"addition isn't a solution to the aura discussion.
The only real solution would be a less deadly enviroment with less powerful creature-destruction spells. The reason for creature-auras to suck aren't the auras themself, but the low survivability of creatures. That's one major part why auras who can enchant a creature an opponent control, don't suffer as much as others.
So R&D should start to calculate things!!!
If you compare a
Doom Blade 
with an aura like
Arrest 
or
Prison Term 
, then the Arrest has a hidden "as long as Arrest is in play" attachment. This textual add-on should reduce the casting cost to balance both cards. But this won't happen, because R&D always tries to keep the status quo and this means that some cards have to suck for limited format and sales reasons.
It's like the comparison between
control magic 
(aura-based control exchange) and
Govern the Guildless 
(sorcery-based control exchange). The aura always leaves a back door unsealed.
Another hidden difference between Arrest and Doom Blade is the casting speed. Whereas the Doom Blade has a hidden "flash" addition, this isn't recognizable in the casting cost. Another call why instants are always preferable. They don't just deal 2:1 with any aura on the stack, the same is true with other enhancing spells as well (see
Giant Growth 
). A
Lightning Bolt 
can take care of the attacking creature and any buff spell targeting that creature. It can even counter abilities with a target once.
To compensate this, you can either reduce the casting cost of aura spells even more to a rediculous amount, or increase the casting cost for instantaneous destruction spells on the other hand. With the mentioned
Lightning Bolt , R&D has proven which way the DON'T prefer. (One reason why I quit buying cards or playing tournaments). A
Chain Lightning 
would have been a much better reprint.
Last but not least, the Arrest vs. Doom Blade has some minor hidden facts. The Doom Blade takes care of continuous effects as well (like "all elves get +1/+1") and enable other effects like reanimation. An enchanted creature (or removed creature with
Oblivion Ring 
) just feels unnatural, since they "waste" space on the gaming table. An annoying fact, if you play in larger multiplayer groups.
Last but not least, even if an aura wouldn't create a 2:1 disadvantage (that could be negated by the "hasty efficiency", one questions is still unanswered:
Is an
Unholy Strength 
a better option than another
Elite Vanguard 
. Sure, an Unholy Strength can create a more powerful creature, but another weenie gives you more options.
With 2x 2/1 creatures, you deal the same amount of damage as with a (2+2)/(1+1), however, if your opponent has a 0/4 wall in play, the higher power could kill the wall, producing a higher damage on the long run. A smaller creature on the other hand allows you to block more creatures and are more efficient to global enhancement effects ("all creatures get +2/+2).
But what wasn't mentioned jet:
If you have no creature in play, and you could either draw an Unholy Strength or an Elite Vanguard, which card would you choose? - Shouldn't be to hard to decide.
So you have another implicit disadvantage for aura cards: "You can't play this card, if you don't control a creature". But where is this effect represented in the casting cost for an aura spell? (the same is true for enhancing instants/sorceries).
A solution for the aura question would take much more than printing "totem armor" on a card. Even a reprint of
Rancor 
wouldn't fix it, if the to-be-enchanted creature still has to fear cmc 1 removals like Lightning Bolt, Path to Exile and similar cards.
@ R&D & Mark Rosewater:
If you really want to make enchantments competitive, first start to balance creatures vs. creatures, then creatures vs. destruction spells, then instant destruction vs. sorcery destruction and finally, you will see, that you nearly don't have to fix auras at all.
And if you did this, you can create cards like
Ranger of Eos 
,
Vengevine 
or "Bannerets" for aura cards instead of creatures. And finally, you will have an easy and flavorful way to make an aura-based block, where players will build decks around
Wild Growth 
instead of
Noble Hierarch 
s.
PS:Start by differentiate between critical creature-denial and non-critical-creature-denial. The first half get's all the destruction spells, whereas the second part sums up all the other options who play around permanental destruction.
Only the last half should have a low cmc and should be instantaneous. One exception: Red - as the hasty color - should keep hasty destruction spells, but at a reasonable cost.
With non-critical-creature-denial, I mean anything that takes care with creatures for a short duration. Things like tapping a creature, -X/-0 effects, forbid an attack this turn, flicker-like effects, damage prevention, damage redirection and so on. If these effects are instants, you could still handle buff effects like a Giant Growth. Some of these effects would be ok for cmc = 1.
Permanental removal however, like pure destruction spells, removals, Oblivion Ring-like effects, discard and so on shouldn't be instants and they should have a casting cost nearly as high as the possible creature destroyed. Killing a cmc 6 creature with a cmc 1 instant isn't funny and doesn't increase design space/possibilities.
There are some effects, that don't fit in either of these two parts:
Effects like bounce, counterspells and
chump blocker instants 
,
Extract 
-like effects, non-specific sacrifice or permanental life-gain can create at least a semi-permanent effect, but have to be or can stay at flash speed. So it should be possible for every color to concentrate on at least one effect from every mentioned part.
And if you balance the minor-instants part, noone should fear a time, when a sorcery Doom Blade would cost
or even
instead, increasing the casting cost in the same way as WotC already did with "unfunny" counterspells (not to mention the absence of multiple land destruction spells). Then a minor-instantaneous-effect + cantrip should still be a bit cheaper than a permanental-sorcery-effect without a cantrip.
And then - an only then - I think, magic will be much more enjoyable than the current metagame with either
"removal+removal+another_removal+planeswalker_with_semi-removal" decks or the
"anti-removal-thrinax+anti-removal-Broodmate+anti-removal-SiegeGangCommander+anti-removal-cascade+removal+removal"deck type.
