Hence my initial suggestion for spellsteal.
High elves ( and blood elves by proxy ) are supposed to be superior spellcasters (having practiced their craft for over 10.000 years), so being able to manipulate magical effects makes sense lorewise (same as enchanting bonus). At the same time ability to regenerate energy or rage doesn't suit them well logically, and, in my opinion, neither does the ability to drain magic from thin air, ever since the Sunwell was desecrated by the Scourge ( otherwise they wouldn't have that addiction problem, would they? ).
From purely technical point of view, that ability benefits all classes and it isn't overpowered. We have to remember that it's only the magical effects that can be stolen, that means the ability is only useful when countering a spellcaster, that bothers to buff himself ( which, in pve content, is about 10% of the fights ). The effect itself is hardly any different from [dispell magic] priest ability, in terms of when you can use it.
But, as I said before, I'm just posting it here as a speculation, I'm perfectly content with whatever we have at the moment (probably because my main is a human paladin).