I think you have the right answer. Why do you say Roman numeral analysis breaks down? You did it just fine with Roman numerals.This kind of harmonic sequence Schumann uses to achieve a particularly poignant and sweet character. It fits right in with the dolce, piano marking at the beginning.Let no harmonic analysis go without a subjective discussion of the effect it has on the ear!Walter Ramsey
Interesting reply! Your analysis is akin to what I remember from Schoenberg's "Structural Functions of Harmony." In this book, Schoenberg grouped harmonies according to "regions," and the Neapolitan was at the center of the flat region of any given key. That would strongly support what you write here.For me, reading "Structural Functions" was an eye-opener, because it made me realize how harmony can operate 3-dimensionally: on several planes at once. The book is confusing at times, and you often wonder how he came up with the Roman numerals that he did (because they could often easily be something else), but his mental image of the way harmony works is unparalleled. I recommend it!Walter Ramsey