I vibe coded for months but switched to spec driven development in the last 6 months
I'm also old enough to have started my career learning the rational unified process and then progressed through XP, agile, scrum etc
My process is I spend 2-3 hours writing a "spec" focusing on acceptance criteria and then by the end of the day I have a working, tested next version of a feature that I push to production.
I don't see how using a spec has made me less agile. My iteration takes 8 hours.
However, I see tons of useless specs. A spec is not a prompt. It's an actual definition of how to tell if something is behaving as intended or not.
People are notoriously bad at thinking about correctness in each scenario which is why vibe coding is so big.
People defer thinking about what correct and incorrect actually looks like for a whole wide scope of scenarios and instead choose to discover through trial and error.
I get 20x ROI on well defined, comprehensive, end to end acceptance tests that the AI can run. They fix everything from big picture functionality to minor logic errors.
Ironically, if you look at Sysco's stock price during the dotcom days, it's often correlated with Cisco spikes because clueless traders would accidentally buy the food logistics company stock instead of Cisco.