The Nix language is cute, very powerful, and as you say, is capable of cool tricks. I personally find it very easy to read too.
For every project I work on, I define a .nix file describing its build environment. It is then just a matter of cloning the repo, typing nix-shell, and then all build dependencies will be downloaded and I'm ready to go. These nix files also specify which emacs I want to use and with which modes: I don't use Emacs' package manager.
I use nix-shell for pretty much everything. My basic environment contains only core utilities. I launch firefox with "nix-shell -p firefox --run firefox" (bound to a shortcut defined in my xmonad config).
Nix is easy to customize. The override infrastructure makes it easy to modify package definitions from your user config file, and I find I am much happier doing this in a programming language rather than a bespoke config file format.
Other pros: you don't need to be root to install stuff. And there isn't much more satisfying than getting a new laptop, git cloning the repo containing your intended system configuration, and being back up with your old OS with one or two commands.
As you say, if Arch turns you off, Nix may horrify. Despite the vote, I'm pretty discriminating about who I recommend it to.