I wrote this, a few years ago, about being careful to avoid "concrete galoshes"[0].
I've found that it's a balancing act; like so many things in software development. We can't rush in, willy-nilly, but it's also possible to kill the project by spending too much time, preparing (think "The Anal-Retentive Chef" skits, from Saturday Night Live).
Also, I have found that "It Depends" is an excellent mantra for life, in general, and software development, in specific.
I think having LLM-managed specs might be a good idea, as it reduces the overhead required to maintain them.