Beyond making a computer "future proof" you should also consider making sure it makes it into the future. Here's my advice:
Purchasing a Mac with a credit card can increase the warranty by a year (up to 4 with AppleCare) as many credit cards add purchase protection services. Be sure to look into the terms of a credit card to see what it offers. I believe all AmEx credit cards offer this, and I've been told many Visa and MC credit cards have this as well. (Protip: pay off the purchase within the first month to avoid debt )
Homeowners/renters insurance can cover accidental damage to your property. Look in your policy to see if you are covered and up to what amount. If you do not have coverage, consider adding it to your plan, or purchase a Square Trade accidental damage protection warranty. (If you live with your parents still, you're covered by their homeowner's/renter's insurance)
Additional RAM will usually be more beneficial in the long run than additional CPU power. As time has gone on, OSes have required more memory to operate, but not CPU power. However, if you can afford to add both, there's no reason not to splurge. (Don't bother with the 2.6->2.7 upgrade though, there's supposedly not a noticeable difference)
While I wouldn't personally choose the rMBP, I agree with others in this thread in that RAM > CPU. That being said, I'm the type that would get both...
If you have the money, get both, otherwise, just the RAM.
For future reference, remember that when comparing RAM to CPU, the CPU will ALWAYS be faster than the RAM in clock cycles, so getting faster RAM is more important. Speed > Size
There's no such thing as "future proof" in laptops. It's honestly an antiquated way of thinking that needs to go.
If you're asking what upgrades will be most beneficial to your experience (that may be standard in the future), then RAM should be before CPU, though if you're an average user you might as well take that extra $300 and buy yourself a nice tablet.
I'll be getting the RAM and CPU upgrades, but that's because I'll actually benefit from them for virtualization.
Think about what you're planning on using this laptop for in the next four years. If its simply surfing the web and word processing, CPU and RAM upgrades are a waste of hard-earned cash.
To get the most life out of your rMBP at the lowest price, go with the stock 2.3 GHz and max out the RAM to 16 GB. Keep the 256 GB SSD, which you will use only for your OS and applications, and buy yourself a fast external hard drive or RAID array for your work files, documents, etc.
If you only get 8 GB RAM and hit your memory ceiling, the OS will start paging out to your SSD drive. While an SSD is faster than a hard disk, it is still only a fraction of the speed of RAM. The difference between the 2.3 and 2.6 is approximately 10%, but if you run low on RAM the performance hit will be far worse than 10%. Most often the performance bottleneck in modern computers isn't the CPU - it's the disk drives and RAM.
Okay, what's the difference between using a base model 2.4 ghz c2d MacBook Pro from early 2008 (non unibody) or the 2.5 ghz upgraded model today?
Not freaking much, especially with the standard 2 gig ram configurations for each machine. Upping the ram to 4 gigs or the maximum 6 gigs would make it more usable for browsing and basic computer usage, and the same goes for a larger and faster hard drive. Professionals using demanding cpu and gpu intensive apps would find the setup somewhere between barely tolerable and unusable.
It would therefore stand to reason that cramming the non-upgradeable ram would be the most important factor in obtaining maximum usability for basic tasks, and cpu speed in the same model family would be the least important. The SSD in today's models MAY be able to be upgraded to larger capacities by 3rd parties like OWC, but I doubt if there will be any noticeable speed difference. And since all 2012's share the same GPU, that's probably not much of a consideration, either.