I think that the whole plastic-doesn't-break-aluminum-does argument doesn't really carry a lot of merit. Samsung, HTC, Sony, Apple, and practically every manufacturer makes these phones with the notion that they're only meant to last two years, since the majority of smartphone users upgrade around the time their contract is up.
So regardless of whether plastic or aluminum holds up better, both are going to disappoint at some time depending on how you drop the phone (which is why the YouTube drop test results have been so variable from person to person). It's the same reason I believe the Xperia Z's "waterproof" feature only goes a long way. Manufacturers purposefully choose materials that are durable up to a certain point on the inside and out. Plus, we all know how lucrative the insurance, repair, and accessory markets are these days, so there isn't really anyone with significant pull pushing manufacturers to change these habits anytime soon.
Both the 'plastic' and 'aluminum' finishes aren't really going to make a difference as far as dropping your phone is concerned, in my opinion.
That being said, I also am inclined to disagree with the idea that an aluminum finish makes a product more "premium," thus attracting buyers looking for the 'most' top-of-the-line product. When you walk into a store and ask a sales representative to direct you to the top-of-the-line phones, (s)he is going to point to the hottest-selling phones with the most features and palatable specs on the market. Aluminum finishes are going to make a difference for a few, select customers - many of whom are aesthetic/design-centric and have already been absorbed into Team iPhone. And regardless, the plastic finish of the GS4 isn't going to drive a significant percentage of consumers away from the GS4 (and, again, we have a reference point: the massive success of the similarly-designed plastic GS3 versus the "more premium" iPhone). The vast majority of buyers don't seem to be offended nor unsatisfied with the Galaxy designs & build quality. And the vast majority of buyers are going to shop for top-of-the-line specs that don't make their brain hurt, anyways (e.g. a massive screen with HD resolution, a camera with a ton of megapixels, and 'cool' features like BlinkFeed or Air View).
So I'm not saying that the HTC One's aluminum finish is not going to make a difference at all - it absolutely will affect how some people weigh the One versus the GS4. But for most consumers, it's not going to be enough to convince them that the One is more superior than the GS4. Mainstream hype surrounding the GS4, coupled with incredible name recognition and a forthcoming marketing blitzkrieg from Samsung, is going to make a difference in moving far more units of the GS4 than the One.
I'm very impressed with HTC's step forward with the One, and primarily for one reason: this kind of inter-market competitiveness between Android manufacturers has driven many to make the best phones in the industry. While I was not taken away by a single feature the One offers over the Galaxy line, I do have to say that it is a beautiful phone that has pushed Sense in a new direction. It suggests A LOT about HTC's future direction, a lot all of us can be excited about.
That being said, I think it is far too early (and far too ambitious!) to claim the One will pass the GS4 in sales. Will it steal some buyers away from the GS4? Absolutely. Will it be enough to pass the GS4 outright? I don't think so...