Cleaned the gutters a while ago and the shingle fungus is getting worse: more sites and more stains. I sprized some general-purpose fungicide on the area over the kitchen:

And down the valley between the north and east slopes:

We’ll see what happens by next spring; I hope the larger moss clumps will take the hint.
However, that short length of copper wire seems to be improving things. Here’s the before:

Compared with the current state, from a different spot:

The intense streaks have vanished, leaving a uniform lighter gray layer, and the upper area near the wire looks, mmm, less awful than the lower areas. I think running copper wire or zinc strips (which I have not found at the big box stores) along the ridge vent will do wonders, although I’m not sure how to anchor either one along the hip joints between the other slopes.