1) you're not the sort of person who buys a new rig every two years, and
2) a $300 PC today will give you exactly the same performance as the one you bought 5 years ago: the minimal gains you get in iron are naturally offset by minor losses in software (which is now built by people with SSDs, so good luck with your little spinning disks...)
The market is now artificially segmented to such a fine level, and moving so slowly at the top, that performance simply does not "trickle down" like it used to. Add to that the move to "power efficient" CPUs (aka: less powerful overall) and you will basically see zero gains if you stick to the bottom of the market.
Not quite "exactly" the same performance. A 20% improvement with today's stuff.
But yeah, its peanuts. A 20% improvement over five years is pathetic. I'm just calling out your hyperbole, in case others didn't see it. Apple had like a 50% improvement in a single generation of iPhones, so a 20% difference over five years is very ignorable.
SSDs and GPUs improved dramatically over the past five years. Well... more specifically... SSDs got dramatically cheaper and retained roughly the same quality. So its worth it to upgrade to SSD or to get a new Graphics Card. But Intel doesn't have any GPU offering, and their SSDs are "enterprise" (aka: overpriced). Mushkin / Crucial are better brands for consumers... even Samsung (although a bit more expensive)
The cores are basically the same within the generations.
A five-year-old Pentium G620 is only ~25% slower than the Skylake Pentium G4520. Both are dual-core CPUs that are cheaper than $100 aimed at the budget audience.
Frankly, the fact that AMD Vishera FX-6300 still easily beats out the Pentium G4520 in multithreaded benchmarks... this demonstrates the absolute lack of Desktop CPU improvements. I'd only recommend the G4520 to someone who is really sure that they care about single-threaded performance (ie: Gamers). Most people will appreciate the lower total-cost-of-ownership that FX-6300 offers at that price point.
The G4520 is a $80 chip, Released October 2015. FX-6300 was AMD's 2012 entry: a FOUR year old chip, now selling for $80 to $90 at Microcenter.
Microcenter has some $0 Motherboards if you buy an FX-6300 from them. That's the kind of benefit you get from buying "old". And since CPUs aren't really much faster, why the hell should you buy cutting edge?
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Hell, why are you spending $80 on a new G4520? Facebook just decommissioned their servers. You can get a Dual socket ready Sandy Bridge 8-core 16-thread E5-2670 on Ebay for $80. Amazon for $70
Sure, that's the top of the line $300 chip in the days of a whole PC being able to be bought for $300. What if you're on a five year old Pentium G620?