I agree that it takes a display at least 65" for 4K to be very noticeable. Although I will say that I've seen some spectacular 4K YouTube demo videos that really looked good on my 55". In reality for most people, it's HDR that provides a more noticeable improvement in what you see. And I can see that even on my 43" Sharp Roku TV. . Are you using a Roku TV or a separate player? If you have a player, lower your resolution to 1080 and it should (in theory) reduce your bitrate. Can't say I've actually tested that, though. Also, with Netflix you don't have to subscribe to their 4K plan. I don't, because as you note I just haven't seen the benefit. So I only get 1080 from them. In Vudu you can choose the resolution you want to watch.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
It's not so much 4K, in and of itself. It's HDR that's really the upgrade that comes along with 4K capability, in many instances. That's where people are going to potentially notice. I say potentially because there are some who can view a stretched SD picture and think it's HD, lol.