Scam? No. On 55 inch and above its noticeable. Day and Night.

On the matter of practicality it is debatable.

As long as we're talking about movies only, you're right. But as soon as it's about gaming and maybe future tv (high quality documentary, good tv shows) then HDR should become one of the major benefits.

In general:

Resolutionwise it highly depends on screensize and how far away you are. 55" and ten feet/three meters plus, there's no benefit from resolution. Hell, i'm really slightly shortsighted and without glasses it's sometimes impossible to spot the difference between scaled 720p and 1080p.

With 80" and more at ten feet i'd definitely go for 4K today though.

There are some other benefits ofcourse. Upscaling to 4K will make any sub 1080p source look better, simply more pixels available to scale to. Plus my current 1080p tv renders everything chroma subsampled, downconverting RGB to rec.709. A 4K tv would at least show the full color information of a 1080p RGB source. And if you use any image settings like color temp, contrast, saturation etc, a 10 bit panel will be better at displaying the results.

You won't be disappointed with a 4K tv, yet whether those small benefits are worth upgrading atm at a premium price, probably not. You don't need to be able to see every individual pixel to see a better picture, however upgrading now might be a bit early. Who knows we'll get full HDR tvs next year or the year after.

Anyway, if my current TV breaks, I'll be replacing it with a 4K tv. No point in replacing with 1080p again. Unless there is some awesome deal on a 1080p oled set. But I hope it keeps working until the dust settles on HDR. Do not want the equivalent of an expensive HD ready set again that turned out not to accept 720p. Who knows which HDR format(s) the Neo and Scorpio are going to support.

If you're watching native 4k content, you'd have to have eye issues to not see the difference. I don't really buy that chart people are showing, either. I have seen plenty of 4k screens with and without HDR and even from a long distance as long as it's real 4k content on the screen, it's a clear difference.

@SvennoJ: That's why my next should be a nice 4K OLED. I'm not in a hurry though.

I have seen 4k video and all can say is wow! There is a difference.

I saw an LG curved 4K OLED at an expo once, showing native 4K content. I must say, it does look better then my Sony Bravia Full HD TV at home.
When you look at the TV's in showrooms in large stores though, it looks like they play a lot of cropped footage. I can't even distinguish a 720p from a 4K display there.

But yeah. The difference will be there when watching native content. But don't feel pressed to throw away your HD TV.

I own a 4k TV and yes, it's hard to spot the difference. I think that it has more to do the content though as it's pretty hard to find quality 4k stuff anywhere. Doesn't mean that 4k is a scam though because when I play a game in 4k on my tv, the difference is huge.

Projectors are a nice way to get a really big image for relatively cheap, but there's something to be said about direct light rather than reflected light.

4K is not a scam but HDR is a much more noticeable feature that makes people say "oh wow look at that". Much of the '4K' content is not pure 4K. Alot of the supposed 4K UHD Blu rays wre finished on a 2K(1080P) digitial intermediates and then upscaled to 4K even though they were filmed in 4K(then downscaled to 1080P). This happened recently with The Martian(terrible movie) where it was shot on 5k, finished on a 2k digital intermediate and then upscaled to 4k for it's UHD 4K blu ray release:

http://www.blu-ray.com/movies/The-Martian-4K-Blu-ray/147430/

4K OLED TV with HDR... Not that is a BIG difference.