My next step is probably to decase it and dry out the boards (somewhat inhibited by the thermostat on my roomate's reflow over being broken). My intuition, though, which is entirely suspect, is that there's a poor connection somewhere on there that's likely gotten worse. (It often had a similar though less severe flicker when attached to the charger and fully charged up.)
So. I'm entirely comfortable with decasing. I'm fine with surface mount. I have a lovely hot air rework station in the basement.
What I don't have is a) a good sense of what components are failing and, more to the point, b) where they are on the dratted board. I have found the one teardown, and need to go over it more carefully, but atm I'm doubting I can pull enough info out of it.
Any clues? This may well turn into "I buy another phone, and then if I fix this one give it to my sister..."