Thank you all, I enjoyed your posts very much -- including blueblades' excellent OP on his "philosophy class" thread.
Where I think Plato was right (after all) is in his basic intuition of the "intelligible" as form (idea): "understanding," I believe, is all about re-cognising recurrent patterns in the ongoing flow of phenomena -- from the shape of waves and mountains to melodic themes, harmonic configurations and rhythmic sequences in music. Without such recognition we are mentally lost, and literally speechless, whereas the mere identical repetition of known and expected forms would leave us bored and unsatisfied. We wouldn't be conscious of change weren't it for the unchanged -- even though what we construe as "unchanged" may just be changing at a different pace, or tempo.
Consciousness starts with the experience of difference, the rub of the other, be it pleasurable or painful. Out of this difference we construct identities to which we ascribe permanence -- a necessary illusion for language, I guess; the flip side is imagination (the "world map" where every "thing," including our "selves," is located). At this level some "understanding," delusional as it may be, seems unavoidable. Can it help being "comprehensive," as in Pascal's pensée # 348: "A thinking reed.--It is not from space that I must seek my dignity, but from the government of my thought. I shall have no more if I possess worlds. By space the universe encompasses and swallows me up like an atom; by thought I comprehend the world" ?
It is delusional and self-contradictory by structural necessity: we can't look at the map from within the map, we can't "understand" the world from within the world, even though for all we know we are within; we do so as if we were outside -- exactly nowhere, like "God". Any amount of reflection makes us artificially alien to the world in a sense.