So agree with @davetron5000 that defects to users are the most important to prevent.
I also agree that a test failure doesn't mean a defect occurred as tests themselves
often just are bad tests that don't test what they should. While you do have to maintain
and think about a test suite, well written tests should be entirely isolated.
The app code you do need to reason about the changes of the code effect other pieces of
the application. So while a buggy tests might be a bit flaky, if it just passes and I am
not specifically working with that test it isn't increasing my thought load while reasoning
about the code structure.
I still think people should maintain and keep clean tests, and unless you are doing payments,