I think 4K has ended up being a bit of a whiff in most respects. I just bought a 60" TV for my living room, where we are about 7 feet from it, which is pretty close (it's the narrow dimension in my rectangular living room), and I can't tell much difference between putatively 4K content and clearly-1080P (from Bluray). It's hard to be sure, because all my putatively-4K content is streaming-based, and there aren't that many sources willing or able to ship enough bits to clearly distinguish between 1080p and 4K.
That is, in a 1080p v. 4K streaming contest, if you dedicate the same larger number of bits to the 1080p content as the 4K content, you'd get a better 1080p signal, too. With lossy compression, pixels aren't directly comparable, they have a quality, and low-quality 1080p pixels v. low-quality 4K pixels makes it hard to tell what differences are the format, and which are just the low quality in general.
(In other news, I consider the idea that streaming is obviously superior to disks to be a bit crazy. What disks have is higher quality pixels, and I expect that to continue to be true for a while. I've seen Bluray 1080p streams that are clearly superior to putatively 4K over-the-internet streams. And I've got DVDs that upscale to a higher quality than putatively 1080p streams of the same content.)
Far more important is the increased color gamut and HDR support, which does provide a noticeable increase in image quality. Even from those aforementioned dubious-quality streaming sources; the higher-gamut HDR images are a visible improvement over the NTSC-sunglasses we were all wearing without realizing it.