I think arguably you have it a little backwards. First and foremost, have you read 'Death of the Author'.? It's an important text on literary criticism about the relevance of the author in the whole process of interpretation anyway; does anything they 'intended' matter? Or does the text gain its 'meaning' from an intersubjective relationship between the words on the page and the reader? (That's a gross simplification, but it will do for now).

Second, you talk about 'media literacy'. So you know that the 'media literate' have awareness of the wider, non-literal and often nebulous context of some words. That means authors can drop 'symbols' in *before* a central theme or idea is introduced in order to foreshadow it and (even subconsiously) lead the reader to an implicit understanding even before anything is actually revealed. Post-fact symbolism is arguably actually a little pointless - a 'mere' artistic exercise. Teaching students to 'read into' the potential meaning of each artistic choice rather than post-contextualising it is an important skill.

Now, of course I recognise your main point about symbolism is not about the technicalities of its operation, but instead the risk of its mis-teaching leaving younger readers disengaged, and for that I don't have too many answers. I don't think it lies with the particular area you're referencing. For me, the single most important element for engagement is to eliminate the 'each student reads a paragraph' section, where poor readers are terrified and stutter their way agonisingly through the text, and good readers are bored out of their tiny little minds and become entirely disengaged (I used to get chewed out by my teacher for reading ahead). Reading out loud is an important skill, don't get me wrong, and there should be time on the curriculum for it, but not at the expense of potentially destroying someone's appetite for literary engagement for the next decade.