Yeah, I think it's the Wanderer Fantasy where Schubert goes mad with the augmented sixth, especially for modulations. I tend to analyse it like you say and how the composer has written it, unless there is a modulation. I've noticed a lot of times the composer will use German augmented sixth of the subdominant (in A major, D, F, G#, Bb) because of it's two leading tones (G# and Bb) to the tonic. Anyway, I think it's a cool chord.
The late Romantic period seems to be the cut off point where I can't make full sense of what is going on harmonically. Strauss, Wagner, Debussy etc seems to be the cut off point. I can recognise the chords, the use of chromaticism and the use of added tones and suspensions and stuff, but I can't find a clear linear progression of keys and how the modulations fit together (and sometimes what key it's in at points). A lot of the time it seems like a series of unconnected harmonies with plenty of augmented and diminished chords for a mystical, restless sound. I can see voice leading is key to these harmonies fitting together and taken on their own they just don't fit.
I haven't been using too much diatonicism in my writing at the minute anyway. I've been studying more the nature of the sounds, and what guys like Helmholtz, Partch, Cowell and Tenney wrote about in returning back to the mathematics of music and using it as a basis for new systems.