I'm not entirely sure if it's a good idea per se, but hell, what's the point in making everything properly lazy if you couldn't. I mean me personally, I routinely use 20-30 flake inputs for large system configurations and I've never really minded this at all. The only real concern I have is that overriding Nixpkgs to avoid duplicates can occasionally break since the dependency may not be ready for the latest Nixpkgs, but this so far has only ever hit me with nix-vim, which arguably should be in Nixpkgs anyways in some form (although I haven't used it in a while so not sure what the status is.)

Because you have to, I searched and found that at least one of my flakes are in there, nix-binary-ninja, which is a Nix flake for the proprietary Binary Ninja disassembler/decompiler. Neat. (FYI though, while I use that, I'm not sure I actually recommend it; it does gross things to make binja use system libraries for better integration, which right now breaks some extensions. Oh well...)