Here's a different take on how much computer to buy
There is a thing as too much futureproofing. I learned this the hard way, and originally thought you could not futureproof too much. I was wrong. I got a 12.1" aluminum PB in 2003, opting for all of the available bells and whistles. My intent was to get more than 3 years out of it. Cut to August, 2011: the PB is still running fine, running fast, a little worse for wear but physically just fine, and that made it hard to justify replacing it.
The real trick is to try to predict when all of the great attributes of the hardware you buy will become long in the tooth all at the same time, because at that point you have a practical reason to upgrade. A corresponding strategy is to wait until a significant hardware or speed advance comes along, and if a new OS comes along at the same time, all the better.
So when the 2011 MBA came out along with Lion, I got one right away. But the PB is still running fine 9 years later. What it could not do is run anything beyond Leopard (also a still-viable OS), which meant I could not access the app store which meant I could not upgrade iWork or iLife, or much of anything else, period. That brick wall became my line in the sand for an upgrade, not obsolescence of the hardware or the OS, both of which are otherwise still lightyears ahead of most laptops out there running whatever (other than Macs, of course).
Had I not bought all of the bells and whistles in 2003, I would have had a PB in 2011 that was actually more ripe for replacement. It would have worked nearly as good for the 8 years that it was my primary computer and would have cost me less, and even though the coming of the iPad also took some of the sting out of having an older laptop, the bottom line is I would have been better off having not bought top of the line (for that form factor) in 2003.
So when I got the MBA, I took that lesson to heart; I went 128, not 256, and i5, not i7, hoping that in 3 or 4 or more years it will be to a level of obsolescence that is significant enough to be replaced by with whatever the state of computing is at that time, rather than still highly competitive. IOW, I did not buy the computer I thought I would need years down the road, I bought the computer that was just right for what I need today and will need for the next few years, and not beyond that.
Cramming all of the futureproofing that is available into the model you buy today can actually end up not being all that strategically sound.
Having 8 GB instead of 4 really doesn't mean very much today, especially when your VM page file is on a super-fast SSD anyway. When it will make a difference is 3 or 4 years down the road, when OS 11.2 and whatever software you are running by then will finally begin to require it. At that point the money (and its interest) that you saved today by not going big can then be put toward a replacement for your ancient 2012 MBA.
