Considering this a little further, does this mean people you no longer want to follow but who you know well enough to not want to hurt their feelings? Ironic that you do not want to hurt feelings, but the daily clutter you get from them only gets in the way and (perhaps?) makes you resent them more for having nothing of value (to you, that is) to say.
To your second point, do you track how many people follow you on a regular basis?
Makes me think how this may tie into the larger issue of why we communicate using these media in the first place . . .