Outdated IO is a point (it sucks not having USB 3.0 on my 2011), but spending 2x cash it "future proof" is a straw-man argument. "Future proofing" is more the difference between say, a $1400 mid-tier 4K with fusion drive vs $1800 for an entry 5K. 30% more for probably 50% longer life with much better speed for the interim.
Depends how far you go. Yes, future proof to a degree, but i see so many people spend say $4-5k on a machine that is just an expanded version of something you could get with much less severe upgrades for 2-3k (macbooks being a prime example of this - compare fully loaded BTO spec to the middle spec apple offer).
If you need that spec TODAY and use it to generate money, go for it. But if that is the case you aren't likely pushing 7 years out of a machine, you upgrade to get better performance ASAP.
As an example of over-buying... when i bought my 2011 MBP, 16 GB of ram for it cost $1500.
18-24 months later, i picked up 16 GB for $300 or so. There is a sweet spot just before where spec improvement has still increased linearly with price rather than price going up exponentially. This is where you are best off buying, and typically this is the middle spec of Apple hardware, or at most default "high end" machine.
Start doing lots of BTO upgrades and price blows out massively for much less of a performance improvement. And this is what so many people end up doing to try and future proof, rather than just spending less today, buying a new machine for the same amount they spend today and continuing to do that. On average you're using a machine that is 1.5 years old across your lifetime, rather than a machine that is 3-4 years old, on average, with outdated IO and lower performance because the gains you get from newer hardware at the same price are usually much more than the gains you get from much more money on the original box.
[doublepost=1501122710][/doublepost]
That said, not buying a fully expanded machine now is not always a poor choice. It depends on the work you are doing now. I recently bought a new work computer (actually the photographer I work for paid for it). It is a completely maxed out iMac (current back in February so now "the previous model") that replaces a then massively expanded "ancient" Early-2009 PM. I need all of that performance now so buying less that the top iMac wasn't a valid option. I expect to need a new computer in ~4 years.
Definitely, if having the additional performance TODAY will make your life easier or make you more productive (i.e., you are using the machine for making money or doing your job) to the degree you think it is worth it: go for it.
Just don't try to buy TOO far into the future "just in case".
Some things are reasonably easy to anticipate: RAM and storage requirements - and these things will give you real world benefits even today. Just be aware of the exponential price increase beyond the sweet spot.
CPUs are a crapshoot. We've had 6+ years of meh. This is unlikely to continue for the next 2-3 years, due to renewed competition between AMD and Intel this year - if you're basing your decisions on CPUs today on the past 6-7 years of upgrades, this may be a mistake.
IO (i.e., external ports, SSD speeds, wifi standards, etc.) do change frequently, and you can have the fastest machine in the world, but if you can't get data on or off it fast enough it's annoying.
