I took a similar step a few days ago. The 15" rMBP replaced a big box Mac (MP 1,1) as well as a 13" MBA. I got good money for my 1,1 and no other Apple offering convinced me:
- MacPro: No USB3 or Thunderbolt, high power consumption, expensive (compared to technology included)
- Mac mini: No dedicated graphic card, disturbingly loud under load (at least 2011).
- iMac: 2011 model w/o USB3 but with screen and overheating problems plus a little overpriced in my opinion (even as refurb) - and neither 2011 nor the new model available for order anyway.
- cMBP: thick, screen with significantly more glare or poor antiglare solution, no price advantage vs. rMBP when upgraded accordingly (plus upgrading requires fiddling which i simply don't want anymore).
- Hackintosh: Was enthusiastic in the beginning, but it turned out that it's much more fiddling than i thought it'd be after the initial setup plus i faced some problems, e.g. with TRIM on the SSD or 10.8.2 breaking the system. Finally it's not a completely trivial task to eventually get a _really_ silent system (the rMBP is not audible when idling or under low load conditions).
As i found i'm not using the MBA as often as expected, i figured the rMBP would make for a good desktop replacement while still being a decent mobile unit with a better runtime than my 2011 MBA.
Data is saved on a NAS (Drobo FS) and i'll be adding a decent USB3 solution soon for fast local storage. Synology NAS could be an interesting alternative, but the better performance is paid for with a significantly higher price.
A decent USB3 hub would be nice to have, but i want to avoid the still existing teething problems when a USB3 device is not connected directly to the computer. So far i settled with a USB2 hub for standard devices like e.g. Sound, Keyboard, Mouse and (non USB3) thumb drives.
Thunderbolt-to-Gigabit-Ethernet adapter is a must - wireless is not nearly as stable and fast as copper around where i live. Adapter works flawlessly.
External monitor: On my MP and the Hack i had 3 monitors attached. For some reason one of those does not work with Apple's x-to-DVI adapters and the other is too old by now, so i settled with one external plus the Retina display. In theory up to 3 external displays possible.
Still pondering whether to invest in a Thunderbolt-to-Firewire-Adapter or not.
Magic Trackpad is a very good complement imho - my only wish would be that Apple eventually offers a backlit (external) keyboard... *sigh*
If Apple should present something really interesting in 2013 in relation to Tim Cook's mysterious MacPro announcement, i might rethink.
And i will keep an eye on how Haswell performs and how the new form factor on the iMac will eventually play out.
Even though the head says that i made the right move, the heart misses the small Air machine...