There is so much wrong here, I don't even know where to start.
Start with Darkspire Aura. Then go to your own post. Then look at the minor exaggerations in mine.
Yeah, Darkspire Aura is good, it's probably the best pact boon out there, but it's not THAT good.
It's not how good it is that's the problem; it's how -broke- it is.
Problem 1: it breaks the rule of "no out of combat buffs". Because DSA is worded as, unlike nearly every other in-combat buff, -not- expiring at the end of the combat, it tempts players to try stupid tactics (like the silly "herd of sheep" thing, or just not having their warlock rest when the rest of the party does) that shouldn't really be part of the game.
Problem 2: it's a bit overpowered even aside from that. This is less of a problem, frankly -- but DSA is just fine if it goes away after five minutes.
Problem 3: Because of the two of these things in combination, someone who -does- manage to abuse DSA by supercharging it (probably because of a GM failure, but the fact that this is very GM-intensive is part of my point) gets an out of puportion benefit. The game never forces you take long -or- short rests (there's no sleep requirement in 4E, oddly enough), so if you can pick your fights, a warlock could supercharge DSA and then hit a BB with a massive damage lead (as long as the BB is forced to attack the warlock with a targetted attack; an interesting restriction, which is why I mentioned soloing above).
Furthermore, I suppose one could simply try and store up aura points, but you would have to do it all without any form of healing beyond potions,
Isn't that what you have allies for? The problem is that this is an option at all; you shouldn't be in a state where if you can conserve your encounter powers for a few combats and not get your warlock too beat up (not unlikely, since warlocks tend to be invisible between turns if they're built for it, and once you've got a few points in your DSA, the GM may very well have the monsters give your 'lock a large berth; yeah, they probably -shouldn't- do this so you are forced to spend out, but hey), you eventually get into a state where you get a bigger benefit (for one fight) than you'd have gotten if you used all your encounter and daily powers in it. (not to mention into a state where you're better off soloing a fight and forcing the monster to attack you than you are letting your friends help. I mean...what?)
Keep in mind that the only healing you get from short rests is the ability to expend surges. In-combat healing (healing word, paladin side effect healing, etc) is typically more efficient, and since your allies in-combat healing will recharge when -they- take a short rest, if you're not getting too beat up, you can afford to wait until they can afford to heal you.
one could theoretically attempt to stack up aura points but doing so puts your party in such an extreme amount of danger that it's probably not worth it.
Are you assuming the whole party has to short rest or not? I don't think that's the case, though that may be the design assumption.
Oh, to play devil's advocate, one argument -for- DSA sticking around until you voluntarilly take a rest or use it up is that doing so forces the GM to have monsters attack you and let you use it -- if they don't, there's little to no reason for your 'lock to rest -- regaining encounter powers, but losing, say, 4 dice of guarunteed damage isn't a great deal, and it's worse for each encounter the monsters leave the 'lock alone, but if you get to spend your damage, there's not actually that much benefit to waiting for a big bad to spend it on rather than a decent non-minion monster; damage is damage (more or less; obviously, guarunteed damage is -much- better on a creature with high defenses or an unusually strong attack). So the RAW does force the GM to let you use your power, which is good. The problem is either players trying to abuse the power (see sheep: forcing the GM to come up with rulings that avoid this particular abuse; something that is mostly unnecessary in 4th, if appallingly important in 3rd) or players who concentrate on stealth+concealment to make their warlock a bad attack target in general specifically in order to let them build up DSA.
In general, ignoring questions of whether the ability is overpowered in general, it doesn't break the -unwritten- rules of 4E if one has DSA expire after 5 minutes, whereas it certainly does if one doesn't.
