The application of theory can make you "dumber," in the sense that you will only notice what the theory has told you to notice. That's my main objection about some standard uses of theory. Theory will be productive when it makes you notice things you wouldn't have otherwise. That's what we think of as the "creative" use of theory. The creative user of theory will notice how text rebels against prefabricated "approaches."
You could make two columns, on the left everything you notice in the text that supports your particular "reading" based on Barthes, or Foucault, or Gramsci. In the right-hand column you could list everything that is bizarre and doesn't fit any ready-made theoretical construct. That would be the "anti-matter" of theory.
It is said that if you don't have theory, you will be relying on an unstated theory, unreflectively. That is true. Not having a theory or not having theory will not make you into a creative reader! In fact, you are likely to have very dull ideas, in the same way that someone who knows nothing of poetry is likely to write a poem about flowers that rhymes.