I also thought 4K was a gimmick - but after comparing UHD to HD sets, the picture does look considerably better even when the source is only 1080p - and when viewing the few programs that are in 4K now, the video is noticeably better.
I set about 8 feet from my 65" 4K set - and it's pretty close to the movie theater experience (which often show 4K video).
But... Prices are still high on the 4K sets, there isn't (yet) much recorded programming available - and no live programming.
4K is more likely to be successful than the push for 3D several years ago - but, like HDTV adoption, early adopters will pay higher prices and have less selection of programs, for a while...
Since I was planning to purchase a new 65" set anyway - spending the extra $$$ today to get the higher quality was worth it, rather than planning to replace the set in a few years. Plus, the Samsung set has all of the electronics in a "One Connect" box, so that even if the video technology improves, I can upgrade the TV to the latest technologies by buying a new One Connect box to go with the 65" display (which is almost all of the expense of the TV).