HDMI 2.0 def matters. Don't get a TV without it.
For the record, UHD is totally worth it, even if you don't have 4K content. The overall picture quality just looks sharper. It upscales 1080p content to UHD. Basically, it will just look like the clearest screen you have seen.
Playing PS4 games on it is amazing. I had my old Plasma hooked up side by side, and it was a big difference. I don't think getting a 4k TV makes sense, if you are just getting it to get it. If you need a new TV, then get one. But I wouldn't pay thousands of dollars for one yet. While the UHD looks great with all content, I don't think it's enough to justify the huge price jump (well, for many people I would say). But if you can find one for cheap that has HDMI 2.0 + go for it. That's what I meant when I said it was worth it.
But for most, it probably isn't worth it yet. I originally shyed away from one, because people kept telling me there was no point with the lack of 4k Content. But I again, think the UHD and the screen quality in general, totally does make a difference. So even 4k aside, it's great.