I'd say for the majority of startups, ideas are a dime a dozen. executing on ideas is really what matters. Just look at some of the most high valued startups today (Uber, AirBnb), extremely simple ideas with relentless execution.
I prefer "Weeks of coding can save hours of planning" because in my experience it´s true. Though he is talking about working on an idea rather than jumping into coding something where the idea is fairly concrete.