As someone who does not mine crypto-currency, loves fast computers, and gaming on them, I find the current crypto-currency mining craze using graphics cards nothing short of a plague. It's like war broke out, and your government took away all the things you love from the market. All difficult times teach valuable lessons, and in this case, it is "Save up and build future-proof."
When NVIDIA launched its "Pascal" GPU architecture way back in Summer 2016, and AMD followed up, as a user of 2x GeForce GTX 970 SLI, I did not feel the need to upgrade anything, and planned to skip the Pascal/Polaris/Vega generation, and only upgrade when "Volta" or "Navi" offered something interesting. My pair of GTX 970 cards are backed by a Core i7-4770K processor, and 16 GB of dual-channel DDR3-1866 memory, both of which were considered high-end when I bought them, around 2014-15.
Throughout 2016, my GTX 970 pair ate AAA titles for breakfast. With NVIDIA investing on advancing SLI with the new SLI-HB, and DirectX 12 promising a mixed multi-GPU utopia, I had calculated a rather rosy future for my cards (at least to the point where NVIDIA would keep adding SLI profiles for newer games for my cards to chew through). What I didn't see coming was the inflection point between the decline of multi-GPU and crypto-plague eating away availability of high-end graphics cards at sane prices. That is where we are today.
I would still like to think that my machine is better off than that of someone whose purchase decisions in 2014-15 were guided purely by the pursuit of the "price-performance sweetspot." A machine with a single GTX 970, a $150-ish Core i3 processor, and 8 GB of memory, would find it rather difficult to play today's AAA titles at recommended settings. To play them at 1080p, you would have to water down quite some eye-candy, and in some cases, even use fallbacks to older API versions (DirectX 11) on some games, for playable frame-rates. In a parallel universe without the crypto-plague, a $300-ish investment on a sweetspot graphics card such as the GTX 1070 would be a quick-fix to the problem.
There is still hope that some day graphics card prices will come down, that repeated crypto-exchange heists and growing difficulty levels will make it unviable for just anyone and their dog with a graphics card to mine coins; and NVIDIA and AMD launch new-generation GPUs at sane prices. Save up for that day. Save big, for when that day comes, build future-proof.
You may not have to aim for an HEDT (high-end desktop) build with some high core-count processor, quad-channel memory, and oodles of connectivity; but the fastest mainstream-desktop processor (which is where the Core i7-8700K and the Ryzen 7 1800X stand today), should do. Pair that with an amount of memory that's at least half of what the processor's memory controller supports. My Core i7-4770K, for example, supports a maximum of 32 GB of memory. I paired it with 16 GB of it. 16 GB is just a quarter of what today's i7-8700K and 1800X support.
With multi-GPU showing no signs of a revival, your next graphics card purchase should ideally be the SKU that's just a notch below your preferred GPU manufacturer's halo product (which are often overpriced). The GeForce GTX 1080 Ti, is an example of one such SKU. Such a card will give you future-proofing for at least 3 years, and game-developers will point to such SKUs in their recommended system requirements lists for the foreseeable 5 years.
DRAM prices continue to torment gaming PC builders, with memory prices seeing triple-digit inflation over what they should be (a 32 GB dual-channel DDR4 memory kit, which should have ideally been priced around $200, is going for $500 these days). While DRAM prices are hot, NAND flash prices aren't. Solid-state drives, which still majorly implement NAND flash (with 3D Xpoint still in its infancy), are the cheapest they've ever been, with price-per-gigabyte dipping below the $0.25-mark for the first time. The world's largest NAND flash memory makers also happen to be the world's largest DRAM makers, so I wouldn't count on SSDs being forever cheap. I would buy the largest capacity SSD with $0.25-ish price-per-GB while I still can.
There may yet be a future for DIY gaming PCs, provided you buy components that are sanely priced right now, and save up for future-proof components as their prices sober up. Sweetspot products turn bitter sooner than you think.