Disused addresses and the impact of spam
Here's something that I've slowly realized, at least about myself: the annoyance and impact of a given volume of spam is disproportionately large on otherwise idle and disused email addresses. The less real volume the email address gets, the worse spam feels regardless of volume. I have some old email addresses that get perhaps one real email every six months and perhaps a spam email every week or two, and I find it teeth-grinding. Meanwhile I'd only find that (low) volume of spam irritating on my main address (which probably sees over a hundred email messages a day).
(In retrospect this is part of why I said postmaster addresses are dead.)
I've previously written about why I feel noisy addresses are dead and while I still agree with the low level mechanics of that, it's not what affects me here (one email message a week can't exactly be called 'noisy'). What I think it is is the ratio of spam to ham. On a relatively disused email address the amount of ham declines much faster than the spam rate while the reverse is true for most actively used email addresses. My disused accounts thus wind up with huge spam to ham ratios; almost everything they get is spam (but not quite everything, otherwise I could just set them to refuse all email).
Which leads me around to the (now obvious) conclusion that for me the annoyance of spam can come either from its volume (having to deal with spam very often irritates me) or from the ratio. If almost every time I see I have email somewhere my reaction is 'oh great, more spam', I'm not in a good place.
(I'm actually somewhat curious what the spam half-life of a disused email address is. I assume that spam volume drops off somewhat, for various reasons, but I have no idea how fast it drops.)