After much mulling, I'd decided the choice was between a Mac Mini, MacBook Air 13", and iMac 27" - wildly different, but justifications for each carried about the same weight. Decided on the iMac as it very unlike my then-newish iPad, the Air lacked power, and the Mini would drive the rest of the family nuts when they wanted to watch TV and I wanted to code.
Six months later, no iMac. Major non-iMac announcement precludes a major iMac announcement anytime soon.
Now MBP-R arrives. Tired of waiting. Options changed.
MBP-R + 16GB is about the same price as the bumped-up 27" I wanted. Clock rate is close enough to not fuss. 4x the RAM. 1/4 the storage, but far faster, and bulk of data served well with external portable drives - accelerated by USB3 (@1TB is about $100). Pixel count about the same. Most of the benefits of the Air without encroaching on the iPad's domain. HDMI port means no-hassle use of HDTV. SD port a la MBA 13". Not the vast real estate of the 27", but about the same shoehorned into a messenger-bag-sized clamshell.
Time to liquify some assets. Craigslist & eBay, here I come. Someone interested in an antique "Naval" katana? (most are at the bottom of the sea...)