Bonus: good tests can also serve as technical documentation.

Though I have to disagree with the notion that documentation is as important or more so than code.
Documentation is certainly near the top of the list and often undervalued. I've worked on a project where documentation was lacking and it was painful to say the least.
Without documentation, changing or adding features can be a nightmare. Investigating bugs and offering support is also very difficult. But without code, you have nothing. No product, no users, no value.

There are (inferior) substitutes for documentation: specialized team knowledge, general technical expertise. These alternative pools of knowledge can be leveraged to create and improve documentation incrementally.
There's no replacement for the actual functionality of your applications.