One thing I wish Rowling had spent a little time on, was the power of perception, as it relates to the Hallows -- the Elder Wand in particular. It seems to me that although the objects in question did have amazing properties, it was people's perceptions that inflated them into something worthy of "the quest" to find them.
Did the Elder Wand really confer such great power, or was the perception of it such that wizards of great power were drawn to it, and led by their greed into killing others to get it?
For example, did the wand really make Grindelwald powerful, or was he already powerful, but made reckless by his perception that the wand made him invulnerable? Somewhere in the book Rowling talks about how a lack of restraint made some wizard or other extra-dangerous....
Voldemort apparently didn't even know the story of the Three Brothers, much less the Deathly Hallows -- he'd just heard about this supposedly all-powerful wand. It was no doubt a really excellent one, but how much of its power was due to that of the wizard holding it, and how much of how it was used, was due to the holder's perception of what the wand could do?
As you note, the only one of the three items that Harry actually used for anything active, was the cape. The ring played no essential role, and the wand was employed against him. Harry basically won without being a master of all three Hallows.
The underlying message seems to be the same as the Dumbledore passed on in Book 1: that it's our choices that define what we are. Harry's choices made him the winner against Voldemort, not his hardware.
It kind of gets down to the core of magical power in the HP universe. One of the lessons from the first few chapters SS is that the “stuff” of magic is unnecessary. Remember Harry makes his hair go back the way he likes it and makes the window disappear without even knowing what a wizard is, no wand, no training, just will power and wishful thinking. Wizards in the HP universe seem to be able to just make stuff go, sure they mostly use their wands for big things but the wands aren’t totally necessary, words are good for focus but they’re even trained in how to cast silently, plenty of “throw away” magic is done throughout the series with no wands, words or even gestures of any kind. All that stuff is a crutch to help the wizard focus. Even non-throw away stuff now that I think a little more, notice there’s no wandwork or words to go with animagus stuff, they just change, that’s probably why it’s considered so hard, it’s big magic to start with but it’s completely crutchless.
And then there’s the psych out factor, a lot of the training the kids seem to go through, especially the Dumbledore’s Army training but other stuff to, is largely to believe that they can do it. Most of the setbacks they have early in any training come from lack of belief.
Which brings it all back to the Hallows, especially the Elder Wand. I think most of the power of the Elder Wand comes from the psych out, and the personal belief. I think the wielder of the Elder Wand gets a boost of confidence, and people facing them get psyched out. This would also explain why the “rules” of the Elder Wand are so inconsistent, if the wielder is over confident and their opponent refuses to be psyched out then the “unbeatable wand” becomes pretty beatable. It’s probably nothing more than a really good wand (whatever that means), maybe with a few standing spells on it that make the holder more resistant to certain things. But given that magic is so belief and willpower driven a wand with a kickass rep is worth a lot, even if there’s nothing at all special about it.
Dumbo.
Couldn’t fly without that magic feather...