You left out the biggest component.

• Design/Research/Thinking/Coding/Testing/Documentation: 10%
• Maintenance: 90%

With that in mind, anything that can be done in the 10% to make the 90% easier is well worth the time and trouble.

I'm all for thinking and research and design, but 75% seems excessive. Then again, I don't make a distinction between Coding and Testing. As bikeNomad implies, my approach resembles more design-one-feature -> write-tests-for-the-feature -> code-the-feature.

You can put a lot of time into design up front, but what if you get something wrong? You can put of the tests until later, but what if you don't remember exactly what you were thinking when you were writing the code you're now trying to test?

Make safe bets.