for a user that isn’t trying to maintain a dev environment, it’s a bloody lot of hassle

I agree but I prefer it to things like ansible for sure. I'm also happy to never have to run 400 apt install commands in a specific order lest I have to start again from scratch on a new system.

Another place I swear by it is in the declaration of drives. I used to have to use a bash script on boot that would update fstab every time I booted (I mount an NFS volume in my LAN as if it were native to my machine) then unmount it on shutdown. With nix, I haven't had to invent solutions for that weird quirk (and any other quirks) since day one because I simply declared it like so:

{
  config,
  lib,
  pkgs,
  inputs,
  ...
}: {
  fileSystems."/boot" = {
    device = "/dev/disk/by-uuid/bort";
    fsType = "vfat";
  };

  fileSystems."/" = {
    device = "/dev/disk/by-uuid/lisa";
    fsType = "ext4";
  };

  swapDevices = [
    {device = "/dev/disk/by-uuid/homer";}
  ];

  fileSystems."/home/mrskinner/video" = {
    device = "192.168.8.130:/volume/video";
    options = ["x-systemd.automount" "noauto"];
    fsType = "nfs";
  };

  fileSystems."/home/mrskinner/Programming" = {
    device = "192.168.8.130:/volume/Programming";
    options = ["x-systemd.automount" "noauto"];
    fsType = "nfs";
  };

  fileSystems."/home/mrskinner/music" = {
    device = "192.168.8.130:/volume/music";
    options = ["x-systemd.automount" "noauto"];
    fsType = "nfs";
  };
}

IMO, where they really shine is in the context of declarative dev environments where the dependencies can be locked in place FOREVER if needed. I even use Nix to build OCI/Docker containers with their definitions declared right inside of my dev flake for situations where I have to work with people who hate the Nix way.