Literally half of what I've written for the site is either apocalyptic or post-apocalyptic, so I'll give my small opinion:
Dead worlds are (sometimes) easy to worldbuild. One thing I discovered when writing All the Dust of Yesterday was that I could convey a sense of a world that was, in recent history, bustling with life without having to actually deal with the consequences of the character having to interact with that world. The old world is gone, so you only need a few melancholy reminders of it. Especially if you only have one character still alive.
Secondly, you could use an incredibly hostile world as a backdrop for goofy shenanigans. Showing a society dealing with a set of ludicrous problems through equally ludicrous means (IE, cybernetic enhancement and underground cities to deal with a planet where the sun vanished) can be really fun if you do it right, I think. I haven't actually pulled this off though so that's very much open for debate. I suppose SCP-3008 also captures this vibe, having people adapting to hostile circumstances in creative ways can be very entertaining, especially when it gains an element of "I'd do this and that if I was in that situation!" for the reader.
Thirdly, apocalypses can be used to set up really interesting dynamics between characters and to explore how people behave when everything goes wrong. I Am Legend by Richard Mathesonis is a good example of this- the book isn't really about the apocalypse, it's about the way the protagonist deals with it and what that says about human nature.
Fourthly, apocalypses are pretty good at criticising things if you want to go down that route because you can literally say that a thing ended the world. Can't have a more obvious theme than that.
As for answering your specific questions, if everything ended a long time ago you are definitely going to have to rationalise why things haven't gotten better again. And magic and technology are always fun if handled right, but that's a complex thing in of itself which I'm not really qualified to answer.
Good luck with your apocalypse!