I must admit I do struggle with 4K. I don't think the jump from 1080p to 4K is all that noticeable than it was from DVD to Blu-ray but it's the HDR that you'll benefit from. Blacks are truly black.
You can always wait for the PS5 and get that as your player.
To me, 4K is only worth it for older movies recorded on film, where you can actually pull extra resolution from celluloid resulting in a more defined image. But even still, it's dependent on the quality of film cameras and film stock used. And out of the Alien and Predator 4K library, I've found the best detail improvements with Predator 2:
With that said, I must admit a 4K upgrade isn't probably worth it for a general, non-fanatic consumption.