Anecdote: although I have spamassassin set up to add a header to my email, my filter for moving likely spam into the appropriate folder is currently commented out, because I get so little spam. I get a very small amount at my public GitHub address, and a little more at one address that is in the source code of a FLO (free/libre/open) app I maintain, but it totals maybe one or two emails a month.

Public organizational emails in orgs I've been a part of (e.g. admin@example.com, community@example.com) get a little more spam, largely sales pitches from what appears to be actual humans at shady SEO companies. Maybe 2 a week.

I get way more "legitimate" corporate spam than actual unprompted/cold spam. The most egregious example in recent memory was when I made an online purchase at Bed, Bath, & Beyond, and made sure the "sign me up for the email list" checkbox was not selected. They sent me no fewer than four emails asking if I would like to sign up for their email list, including one titled, "Thanks for signing up for our email list!" (inside: "Just take this one last step to confirm your subscription <signup link>").

In conclusion, I perceive unwanted email to be largely a self-inflicted problem at present. For example, someone I know likes to complain about the quantity of email she receives, but also refuses to unsubscribe, because sometimes she sees something interesting in one of the many promotional lists she's on. I also don't understand people who say they're not bothered by advertising, but to each her own.