This is probably a pretty good read on the situation. People who have really thrived with Nix are often at the intersection of 'FP people' and 'extremely stubborn Linux people', and that's because sometimes it takes getting your hands dirty and fighting a build system that belongs to a package you've never used before to get the Big Ideas to pay out. When the footwork is already relatively familiar to you, it makes it easier to push through whatever obstacles there are to playing with those attractive Big Ideas in practice.
The Nix community's roots are definitely with FP people, partly due to the language and its inspiration and design, and partially also due to early success using Nix to solve particularly painful Haskell dependency hell problems years ago. All of the original 'marketing material' for Nix focused on principles and properties that would be attractive only to people who already knew and valued those things, which was mostly FP folks.
> Perhaps [Nix] will influence more mainstream projects, bringing the benefits to me without a lot of upheaval.
This is definitely already happening. Off the top of my head, Nix has served as inspiration for Guix, Habitat, and Spack, which are all respectable package managers that try to make things a little smoother than they are with Nix in terms of UX. The latter two are also more conventional, with a relaxed notion of 'purity', and so it may be easier to get packages to build in them when those packages are built in problematic ways. (Guix, if anything, is even stricter about packaging conventions than Nix, but it has a really nice CLI and the language might resonate more with some people, so if Nix has given you pain it's definitely still worth trying.
> Perhaps I'll have a project that really needs its particular benefits, and so I'll take on the cost of a paradigm switch. But in the meantime, I have stuff to do.
I love Nix and its fundamental design, and I want to see it flourish and grow, both in general and in my own professional life. But at work, I try to maintain the same attitude as you describe here. I use Nix for myself everywhere I can (with some escape hatches in place!), but for projects that others work with, I only use Nix where I feel that some specific aspect of the project calls for it.
All of that is just to say that even to some folks who really are drawn to Nix in substantial part due to the Big Ideas that power it, your pragmatic stance is quite understandable and entirely welcome.
Feel free to just play around with Nix in a low-stakes way and advance your usage as curiosity or new problems drive you to do so. You don't have to jump all the way in to benefit from Nix or get a taste of it.