I just pulled the trigger and bought a refurb Oct. 2013 13" rMBP. I'm upgrading from a 2011 13" MBA.
The huge bump in performance, increased RAM/HD space, better battery, and the VASTLY SUPERIOR display on the rMBP made it an easy decision for me.
Size wise, the newer 13" rMBP and the 13" MBA aren't too far apart - almost similar dimensions, but the MBA is about a half pound lighter.
Also, I think the rMBP is going to be more "future proof" as opposed to the MBA as programs continue to demand more and more from the hardware.
And the Retina display is a MUCH better display to stare at all day, especially if you're used to looking at the Retina display on an iPhone.