update… I decided to just do a global replace for "Serial." -> "//Serial." using bbedit. After unreplacing the one include for the serial module itself, I did another compile to compare. This was while leaving the debug define alone and enabled.
Before commenting out Serial. everywhere: 32k
AFTER commenting out Serial. everywhere: 38k
so, commenting out 244 serial commands led to an INCREASE of 6k in sketch size.
does anyone have a clue why this is happening?