There's a lot of factors to consider...what you'll be using it for, how long you'll intend to keep it, and how comfortable you are in cracking open your case and upgrading if necessary.
If you're not really a DIY guy, the rMBP's specs look like they'll be good enough for a while, and aren't scared by cutting edge technology or need the best display and/or maximum portability possible, the retina's pretty hard to beat.
If saving the maximum amount of money and getting the longest life possible out of a system (upgradeability) is your biggest concern, your existing purchase MAY be the way to go.
Putting the retina display issue out of the way... the 2011 and 12 classics can be cheaply upgraded to 16 gb of ram, and storage options are consistently improving for consumers; newegg is consistently sending me daily specials about SSD drives...I'm seeing reputable 256 gig drives going for as little as $180 and 512's for $400 and up! It's also quite possible to jettison the superdrive,but to use that space for additional storage instead of shaving size and weight off the chassis like Apple did. I wouldn't be surprised to see 1TB SSD's being sold for $500 or less in two or three years*, assuming that other PC makers don't follow Apple's lead and make their own portables completely consumer unserviceable.
Every day is not all strawberries and orgasms in upgradeland, however. A single whoopsie could result in repairs coming out of your pocket or having to replace your machine. You may spend a good hour installing upgraded components to discover that one of them was a dud. There could be a problem updating firmware with your 3rd party device. And if there's a problem you have to have fixed while within the applecare warranty period, you'll either have to dig up the original components and reinstall them, or risk the tattooed, pierced genius** behind the counter at the back politely giving you the finger and refusing to authorize the repair; and maybe even claim your unauthorized install damaged your machine and void your warranty.
Either option has compelling pros and cons and is largely subjective. Do you want a platform you can keep for as long as possible with extra time, effort and money, or would you rather fancy a low maintenance, perfectly usable internet and computing appliance? Like many of the tough questions in life, the answer is contained within yourself.
*But I would be completely delighted!
**Maybe it's just my own local apple store. But everyone there save the business guys have facial hair, piercings and copious amounts of ink. Is Apple opening recruiting drives at Burning Man and local Renaissance Fairs?
