Thanks everyone. I went with the 13" rMBP. In addition to the stuff mentioned already, the build quality is noticeably better. It simply feels sturdier--with a smaller footprint. It is a touch heavier, but not dealbreaker heavier at all. And the screen is exceptional. Retina definitely makes a noticeable difference to me. And since I'm doing more writing these days, that is nice. I was concerned about having less screen real estate than on the MBA, but then realized that I have a 27" iMac for that. So this was the way to go.
I tried hard to make it lag in the store and couldn't. We'll see about Aperture, but that was laggy anyway on my MacBook so I'm sure it won't be any worse.
I got 7 years out of my iMac and 4 years out of my MacBook and they both are still serviceable for other tasks. Macs fuckin' rock.
And, yeah, AppleCare.