I had/have to use vim almost every day (a lot of it was managing headless servers, but also being a linux user myself), and it was somewhat of a pita every time I used it, but a bit less so than nano, pico or what have you.
After some time I finally had enough and decided to invest some time in figuring it out mostly in the hope of making it a bit less of a pita. Also, so many people seemed to just love using vim. Makes you think that it may not be the most pointless thing in the world to invest some time in.
What I got from it personally is:
Most text editors now feel like there's not much to them, you rote learn the editor specific shortcuts, but they often don't have any meaning on their own so there is a tendency to forget them when they aren't used every day. Luckily the ones used most are often somewhat consistent across editors so it doesn't take much time to get to some level of proficiency with a new editor. Also you often have to use your mouse and sometimes arrow keys for efficient movement and text selection. This requires constantly moving one of your hands out of the typing position which seems a lot more distracting if you get somewhat used to "mouseless" text editing.
With vi(m), yes, you have to learn the shortcuts/commands but they kind of add together, almost every command or way to do something seems not only useful by itself but also expands your vocabulary and enables you to tell the editor what it should do in a more efficient way. In a way you are making up shortcuts on the fly all the time by composing commands you know depending on what you want to do, only most of the time (at least while editing text) you don't actually think about commands or shortcuts just like you don't have to think about ctrl+x and ctrl+v, it's just select, cut, paste.
tl;dr, my opinion
Is it worth spending the time and effort given the steep learning curve?
If you don't already use vim at least some of the time and would have to force yourself into using it, I personally would say no. I think I still would have tried it but I don't know if I would have stuck with it once the novelty had worn off. I wasn't really unhappy with text editors, I just didn't like using vim the way I was using it. Also you end up adding "vim mode" plugins to every damn thing you type text into, IDE's (used for those behemoths), other text editors, web browsers, ...