I say this as someone who never quite warmed up to Jed Lowrie and his pasta-diving, called third strike complaining ways. But if you have a chance to acquire Lowrie, now 31, for your #30-ranked, unproven prospect, on a 2-year, $14M deal, you pull the trigger whether it fills an identified need or not.
Let's start by talking about what you are getting when you add Lowrie. Yes he's coming off of a down year at the plate, but having watched him for two full seasons and followed him for several more, I would describe Lowrie as a hitter who has unusually good plate discipline as well as good power for a middle infielder. He is capable of putting up around a .350/.450 line, which you would gladly take from a 3Bman and would love up the middle.
We know, all too well, that Lowrie's range is no great shakes, his arm provides the noodle for his pasta-diving, and that he is an "offense-first" type of player. However, with good hands and strong fundamentals he is adequate at 3B and 2B, serviceable at SS.
Essentially, when I think of "adequate at 3B and a .350/.450 batter" I am describing what Danny Valencia provides when he starts against LHPs. Lowrie, a switch hitter, basically gives you a full-time Valencia while at the same time making either Valencia or Brett Lawrie available to trade as the A's seek to address other needs.
Another way to look at it is to ask, "What if Lowrie had been available to sign, as a free agent, to a 2-year, $14M deal?" Would you want the A's to do that? My answer is "Heck, yes." And while McCurry emerged as an intriguing prospect rising through the minors, you are not going to let him be the difference between that "free agent signing" and walking away.
Objectively, just based on his pedigree and having logged all of 16⅔ IP at AA, McCurry's likeliest career outcome is "never throws a big league pitch," while his next most likely outcome is "has a nice season along with a couple cups of coffee". Every prospect is a roll of the dice who could turn out to be Josh Donaldson or could turn out to be Richie Robnett, but judging the trade at the time it happened one is inclined to conclude that the A's just got a versatile infielder with a good bat, with an affordable contract, almost as if they had been given the opportunity to sign him on the open market. And I would make that signing any day of the week and twice on Sunday (because who wouldn't want to have two Lowries and one Lawrie? Isn't there anyone named Larry we can get?)
None of this is convincing if you feel like Lowrie is a "DH-only" or if you don't think he can hit well. I am looking at the possibility of adding an above-average hitter who can play an average 3B or 2B and I think that makes the team better while also setting up another helpful trade. And he must be pretty good if I am willing to praise him, considering that I graduated from Cal. Go Bears! But still a good trade.