I have a pre-4K Apple TV, and I have the latest version of Apple TV 4K. I cannot at all tell the difference between the two at all. I think one even has 32 GB and I've never run out of space. That's about 10 years of "advancement" in Apple TV where it doesn't amount to anything.

And yet I have 4 of them in total because they are much better than the built in apps and I don't trust the TVs to connect them to the internet. It's basically CarPlay for my TV but does an excellent job because of the consistent interface and good apps.

I am in no hurry to get this latest version.