I said this in another thread about 4K. It removes all the jagged edges from lettering and sports overlays. Between the contrast that comes with a 4K TV and the additional pixels, the image just appears sharper. It's not nearly as tangible as the upgrade from SD to HD but it is there.
That said, there is no long distance HDMI 2.0 on the market as far as I am aware. HDBaseT is still waiting on the HDBaseT 2.0 refresh which I suspect but cannot confirm will contain enough bandwidth for 18Gbs HDMI. If you look at the HDBaseT specs, I'm pretty sure all of the products on the market today will be limited to 10.2 Gbps. What that means is that you will get 4K 8bit 4:2:0 color @ 60Hz and 4K 12bit 4:4:4 @ 30/24Hz. HDR is not supported. It sufficient for 4K today but probably has a lifespan of 2 years before the big (70"+) HDR/WCG displays are in the $3K range. If you're playing in the $10-15K TV space, you may be able to find something cutting edge for a grand or two that will do 18Gbs HDMI.
While 4K is an upgrade in image quality, you have to know that you are buying bleeding edge and the full solution may not be there yet. You also need to know that you might replace what you bought inside of two or three years if you want to get the full 4K experience once the dust settles on the specification.
The only thing holding back 4K technically, is physical cable technology that is married to the HDMI specification. That's what is giving you the feeling that your 4K TV purchase today will last. 18Gbs HDMI and 36Gbs DisplayPort are short cable runs only which massively limits the ability to send video anywhere other than the TV sitting on top of the sources. The latter doesn't have HDCP so it is a non-starter in the CE world despite being the faster specification. So there's this looming question about signal transmission with respect to the future that appears to be a year or two away. (maybe more) Something will have to give for TV to not die at the 4K @30/60 Hz resolution. (Fiber, HDCP Added to DisplayPort, ...) When that happens, all the gear you bought today will rapidly become obsolete. 8K has no chance at happening without making the move to some other means of signal transport that can readily support the bandwidth.