we've tried pruning them down, adding pine needles, and cutting a few branches to open up more sun (still probably too shady), but they haven't made any flowers the past three or four years. Because we have new blueberry bushes for free I'm going to take out the old ones and offer them to a new home. I know they can be used for cuttings, though I don't know if the new plants would be healthy or fruitless--will they be fruitbearing?
But in Maine, seaweed is gathered and used as mulch along with pine needles for the blueberries, and the blueberries flourish like crazy. Other people successfully use kelp with blueberries, also. Not knowing how acidic your soil already is, you'd probably have to experiment with applying a diluted amount of kelp tea, and compare that to one with vinegar added. You could also just mulch with a little kelp meal along with your pine needles and see what that does. But kelp and other seaweeds have beneficial components in them that can't be found elsewhere.
Location: Massachusetts, 6b, suburban, nearish coast, 50x50, full sun, 40" year-round even distribution
update--they're fruiting again. Go figure. A tree came down that had been shading some of them (but not all), and I did add some mulch to them, but I really can't explain it, they just seem to change their minds).
Community Building 2.0: ask me about drL, the rotational-mob-grazing format for human interactions.