Most of the features I develop aren't good ideas in the end. Writing a test for a feature that you are going to dump after testing it with actual users is a waste of time.
Once a feature has proven its worth, I write tests to protect its value.
the problem with your argument is the hidden assumption that writing tests wastes time, when in practice it usually saves it. Long term benefit of tests is rarely denied, but as many of the TDD people can tell it usually saves time even in short term. when you develop a feature you are testing it, manually, by refreshing your browser and sometimes performing non-trivial sequences with it. Writing tests to do just that can save you time and leaves you with a better code.
Most of the features I develop aren't good ideas in the end. Writing a test for a feature that you are going to dump after testing it with actual users is a waste of time.
Once a feature has proven its worth, I write tests to protect its value.