You know what attribute of a code base is more valuable than any other? Maintainability.
Every project ever should emphasize maintainability over performance, cleverness, etc... because this is the true long term cost of code. If it's difficult to understand why or how something is how it is then you'll pay a lot more to bugfix it and improve it over time.
This attribute is opposed (mostly) to flexible prototyping so a really good senior dev will be able to transition a greenfield project into one that's structured for long term usability.