In my particular case (main module + many plugins), having no repetitive changes implies that (1) API is very stable, (2) extending the module requires little to no boilerplate, and (3) writing tests for the module requires little to no boilerplate.

And having that level of design skills implies posting to p5p rather than SoPW :)

EDIT: From Wikipedia:

In computer programming, a code smell is any characteristic in the source code of a program that possibly indicates a deeper problem.

And, yes, the repetition in plugins indicates a deeper problem with my code, which is: I cannot design a succinct, feature-rich, and testable module interface in one go. And while I'm solving that problem, I'd rather have my imperfect code nicely organized, which is why I'm asking...