Back in November, when we were looking at all the ways the A's could solve SS, Jed Lowrie was kind of a "holy grail". That's because SS is a weak position throughout baseball right now and almost everywhere you turn to look at a SS you find someone who is not very good, or if they are good you're certainly not getting them without emptying your farm system.
The free agent choices pretty much came down to two guys: Slim and None. You could squint at this free agent or at that trade target, and you just couldn't come up with a way for the A's to be good at SS when the dust cleared. Maybe "passable" and maybe "well at least we didn't lose a bunch of guys to get him" -- but not above average.
And then there was Lowrie: A guy you might actually be able to land, who because of a series of somewhat flukey injuries might be obtainable for only moderate talent, and who is actually a good SS on both sides of the ball. He can hit and he can play a good SS.
Now the signing of Hiro Nakajima turned our attention away from the SS position, but Nakajima comes with question marks on both sides of the ball -- especially defense, where it is unsure whether he is a major league SS in fact, or in name only. The A's think he can hit but he has yet to prove it, so that's no slam dunk either.
So yes it hurts to lose Chris Carter. And if you believe Brad Peacock will be a "solid #3 SP" then that's a big loss too; whereas if you believe he will be a "good relief pitcher" it's not that big a loss at all. Max Stassi is a nice prospect, but hardly a "selling the farm" level one.
You have to give up talent to get talent, and the A's most definitely gave up talent to get Lowrie. It's when you remember how good Lowrie sounded in November -- and he hasn't gotten any worse since then -- that the trade starts to look good.
A final thought: Most players who are "passable but stretched" at SS make for very good defensive 2Bmen. If Nakajima can indeed hit, don't be surprised if he's in the 2B mix before long. We have no idea how Scott Sizemore's knee will respond to the rigors of playing 2B and Nakajima has a chance to be much better than Weeks. The A's have a lot of options right now, and that's always a good thing.