So it seems my observations are correct.
Old Honda = great build quality
New Honda = sh1te.
As for the problem of discolouring downpipes, they're metal, they get hot, they discolour.
They get spots on them from bits of tar and other debris hitting them and burning on.
That's what they do.
If you really want to clean them back to unused shiny stuff, try wonder wheels, 0000 grade wire wool, solvol autosol and a bucket of elbow grease