I think there are (at least) two fundamentally different ways to create UIs, suited for two fundamentally different types of UI applications:
Programmer-driven for "tools" (think Photoshop, Maya, IDEs, debuggers), and artist-driven for "user applications" (think typical mobile applications and games).
For the first type, "maintainability and functionality" is more important than "beauty on the surface", and it's also important to give the programmer a framework which encourages "best practices", so that the result is not an archetypal "programmer UI".
Only for the second type, "shininess" is more important than everything else, this includes general aesthetics, colors, animations / transitions, etc...
Programmer-driven for "tools" (think Photoshop, Maya, IDEs, debuggers), and artist-driven for "user applications" (think typical mobile applications and games).
For the first type, "maintainability and functionality" is more important than "beauty on the surface", and it's also important to give the programmer a framework which encourages "best practices", so that the result is not an archetypal "programmer UI".
Only for the second type, "shininess" is more important than everything else, this includes general aesthetics, colors, animations / transitions, etc...