A volume slider per feed, and perhaps also a global one.
If a feed is posting too much stuff, but I still like some of the stuff on it, I'd prefer not to unsubscribe if I had a better option.
If I notice a feed getting a bit noisy, I'd like to open a view for that feed, with titles and timestamps. Then I'd just move a slider and watch stuff drop out, until I've turned it down to a volume I can handle.
Hopefully, the lower-signal items will drop out of view first and the higher-signal items last. The more data available for making these rankings, the better. Comment counts or scores from the hosting site should help. So should links/shares/likes/comments across the major social networks.