One strength of nixpkgs that probably appeals to Arch users too is how much software is available and how easily you can just re-compile apps with custom patches. In fact, the latter is enabled exactly through reproducibility :)

That said, cool if pacman and AUR work for you, no need to change just for the sake of it!

Yes, AUR is one of the things that brought me to Arch back in the day. I was really tired of building and maintaining my own .debs.

I'd say Nix is even easier than pacman/AUR from a maintenance perspective because you can create overlays for whatever you'd like to change and not worry about the mechanics of building your own packages. The overrides are just maintained in the flake or nix config. Also there are already a huge amount of packages in the nixpkgs repo (probably more than base Arch + AUR.)