Vanishingly few things have intrinsic value. The concept, IMO, is not relevant.
Their subjective value is essentially that they are an end in themselves, or rather that 10 levels is too few for certain games and preferences while 20 takes nothing from anyone.
As above, but to be more specific, having more than ten levels, that is points of advancement wherein you gain new abilities or improve existing ones, usually as a group, allows for a longer “zero to hero” campaign, longer “this will take years IRL to complete and when it’s done we will have changed this imaginary world in ways that don’t feel forced or rushed or weird (oh you became an archmage in 3 months…huh), etc
All of the above.
And if a game has 10 levels, but then regular intervals at which you can improve things…but doesn’t say they’re levels…

just call them levels.
My preference for 5e would be to not have a levelcap, make epic stuff sit to the side of class and normals levels rather than being “epic levels”, bring a lot of the new ability stuff down a few levels at the top end, and past about level 15 you’re improving things or gaining mythic traits with little or nothing to do with your class.
Then make levels ramp up power much more linearly, putting a lot of high level stuff into mythic traits (like the ability to learn and cast 7th+ level spells, and most base class endcap features).