I believe conventional interpretations of "Pierre Menard" are mistaken. The point was that creativity belongs to the reader rather than the writer. (This was what we were taught in the 80s.) Menard's version becomes more interesting than Cervantes's because it comes from an early 20th century writer. This is what we learn from Rodríguez Monegal and other interpreters, but it is utterly wrong.
(The reproduction or "transcription" of the text is a narrative device that Borges needs to explain that Menard does not copy the text, but somehow comes up with it through another, unexplained method. This device is necessary to the story, since otherwise the Quijote of Menard would be dull copy with no interest at all. It is not true, as Thomas suggests, that "The point (I thought) was that he writes it in the ordinary way after having gotten his own mind exactly where Cervantes' had been." The point is that his text is identical to that of Cervantes's but his "mind is completely different. In other words, he does not "become" Cervantes.)
The first thing people miss is that the narrator is not "Borges," but an anti-semitic Frenchman. He makes nasty remarks about the other interpreter of Menard's legacy, a woman who has had the misfortune of publishing in a journal known for its philosemitism. This is the France of the Dreyfus affair.
Menard himself is a minor follower of the poet Paul Valéry. The list of his publications is quite extensive and interesting. Curiously, the standard interpretations miss the fact that his "visible" publications are a kind of compendium of Borges's own translation and author theory.
Anyway,the overt argument of the anti-Semitic narrator is that Cervantes's own text is somewhat dull. The example used is the discourse about the superiority of arms over letters. This conventional early modern wisdom is turned on its head by Menard, who certainly cannot hold these beliefs ironically. Voilà, the text means something different when ascribed to a different authorial subjectivity.
This is wholly wrong, though. Cervantes's characters already speak ironically, even when they spout conventional wisdom, since Cervantes is engaged in satire or the skewering of this wisdom. Of course, the discourse on the superiority of arms to letters is put in the mouth of a fictional character, so it is not "Cervantes" saying this.
Furthermore, Borges is a great admirer of Cervantes and, especially of Cervantes's metafiction. See "Magias parciales del Quijote." The choice of a seemingly conventional part of his discourse, the explanation of why it is more noble to bear arms than to read books, is a deliberate misdirection.
To really understand "Pierre Menard," you have to be more Borgesian than Borges, in other words, don't accept the facile interpretation of the text. He was a man unfit for military action whose works evince a strong nostalgia for the violent exploits of his compatriots and ancestors. That places the conflict between arms and letters in a different context.