So I watched Linus' Intel CPU Buying guide, in which he recommended i5 6600K for the gamers and i7 6700K for the 'budding content creator'.
But since it was such an exhaustive list, I think that including the non-k variants wasn't a bad option.
The reason is that it's not just the 10-15% cost on the K variant CPU that you have to pay extra, but you also have to include the price of a good cooler, and a z170 motherboard (as opposed to a b150 motherboard. which I think is fine for people on a budget who don't want SLI, RAID, OCing), so when selecting a K variant for the advantages it offers, one also has to keep in mind the cost of other components if they want to get the full advantage of an unlocked variant.
One also has to keep in mind how much they'll be able to overclock, for example, the place I live in (India), the ambient temperature goes up to 45 C, so I am sure I wouldn't have been able to overclock as much as other people.
The difference between the performance of non K and K variant is minimal, as even though 6700K works at 4.0 base clock, it has turbo of 0/0/0/2 (only one core upto 4.2 ghz, no turbo at even 2 cores) as opposed to 3/4/5/6 of 6700 (all cores turbo upto 3.7ghz, one core upto 4.0 ghz).
I just purchased a new PC recently, and I was aiming for i5 6600, but then upgraded to i7-6700, both non K variants.
My final price of components turned out to be INR 90,000, which is around $1350 (excluding SSD, HDDs, PSUs which I had earlier).
Now had I wanted to get a K variant CPU, I'd have to spend around (at least) $210 more for being able to OC properly, and even then, I'd have been able to get around 5-10% of better performance in benchmarks, and almost minimal real world performance gain. $210 is a significant amount which can be used to upgrade other components (I went from GTX 1060 to 1070), you can even save that amount and upgrade your PC earlier in future. And I am not even going to add the 40% extra TDP of the K CPU, but that could have an impact in the long run.
Now Linus did mention better resale value, but I think it depends a lot on your situation and whether you're able to get a good deal or not.
$30-$50 USD may not be much for you, but keeping in mind the budget conscious, I think it'd be a better idea to save that amount if it's not going to give a justifiable benefit.
So my point is:
1. Getting a K variant only increases around 15% on the cost of CPU, but to utilize that amount, you'd have to spend around $200 more.
2. A Non K variant can be a better option for majority of people.
3. In an exhaustive CPU buying guide, Non-K CPUs should also have a place.
I hope I have been correct in my analysis.