Off top the 4x in resolution may not be as noticeable as the jump from DVD to blue that is correct, but HDR is the difference maker.
Even watching Netflix shows with HDR enabled you can see the difference. HDR specifications weren't/aren't finalized and there's been many upgrades to firmware etc but I can definitely see the difference between 4K and 1080. 720 is damn near unwatchable now.
The biggest difference when I first got my tv was watching a show on Netflix in 4k and then switching to my 1080 tv and continuing to watch it and it looked pretty ugly. Your eyes have to re adjust to watch 1080.
I feel for brehs that bought 4k TV's pre 2016 since they don't have true or any HDR and are missing the whole point.
If you've seen say The Grand Tour on Netflix with true HDR then you wouldn't be calling it a "marginal upgrade"
Here's a shytty example since they cannot properly capture 4k images yet from discs so people take pics with their phone and we're viewing these on 1080 monitors
See how the sky details pop as well as the colors.