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The main problem of the MacBook Pro with Retina display is that you can't replace anything except the flash storage (and it's very expensive). If you want this computer, you have to order it with the storage and the memory you think that you will need.
I recommend the non-Retina MacBook Pro for near all users because of that reason, and the price. There isn't an enormous performance difference between them, but the flash storage of the MacBook Pro with Retina display makes it faster. Another pro of the MacBook Pro with Retina display is the HDMI port and its display, that doubles the resolution of the non-Retina MacBook Pro.
Except you need the Retina display and a light Mac, the non-Retina MacBook Pro is your computer. Apart from that, you can install the memory you need and replace the hard drive without voiding the warranty
For most of the last 10 years I've found it more economical to buy a low end Mac and sell after 2 years - with AppleCare I always get a good resale price. Given that, if the retina Macs hold their value as other Macs do, I don't see a problem with them lacking upgrade paths. What concerns me at the moment is that the high density graphics forces the GPU to push about 4 times as many pixels as the standard displays. For the 13" model especially, there are some noticeable graphic slowdowns. At this time I consider the retina screen to exist for bragging rights, not for improved user experience.
My pocket voted by choosing against the retina Mac.
I think that you have to buy the computer when you need it. If you don't need it now, you can wait until Apple releases a new MacBook Pro, but you may be waiting for a lot of months. You can take a look at some Mac shopping guides as the MacRumors one to see if it's better to buy a MacBook Pro now or wait until a new computer is released, but you don't have to rely in those guides because Apple may release a new one at any moment, so it's up to you
I have a mid-2009 17 inch macbook pro, I upgraded the RAM from 4 to 8 GB, later on I purchased the OCZ Vertex 4 512 GB SSD drive and installed it myself, This computer is freakin' fast ! boots up incredibly quickly and I've had no problems with it.
I like the fact that the non-retina macbook pro's can be upgraded by the user, you can actually replace:
you can even remove the dvd drive and install either a blu ray drive or extra-hard drive
About, support, You can rest assure that Apple will sitll provide support to non-retinas for a long time as they still sell them, that assures at least 3 years of support (that's the longest you can get for the apple care).
Nevertheless, let's analyze the things you can and can't replace on the retina and it's hassles:
The battery: You need to take it to an apple store , they will do that for you (it's glued, don't even try !)
The hard drive: You can replace it yourself, links at the bottom of this reply.
The ram: You can't replace it, it's soldered to the board, You can only choose the amount of ram at purchase.
In addition to that, there are some problems on some retinas (image retention) going on right now, I would wait for the next iteration if you don't want to run into problems...
Apple should upgrade the dvd drive to blu ray drive and put the retina display on the "classic" Macbook Pro, This would be my dream computer. Best of both worlds.
I hope this helps.
hard drive for retina link:
how to change hard drive on retina link: