Anti-spam work is pure overhead
Here is something that is perhaps obvious, but still worth mentioning: all anti-spam work is in a sense pure overhead, in that it is time and resources spent fixing a situation to return it to the way it was before the spammers showed up. Anti-spam work does not actually improve email in a broad sense, it just makes it as not-bad as possible.
(It is possible that anti-spam work will lead to techniques that improve email overall, perhaps better ways of automatically sorting and organizing email, but if it happens it will be a serendipitous side effect.)
This is one reason that I am out of the anti-spam game; I have come to realize that any anti-spam work that I do is 'wasted', simply time on a treadmill in an endless race to stay in the same place. While the race is necessary and vital, running it has ceased to be very rewarding or motivating for me and I am just as happy to let other people grind away on my behalf.
I suspect that people who are immersed in the race do not feel this. Because they are actively doing things, they are getting lots of feedback and so feel that they are clearly making progress; they are blocking spammers, seeing their clever techniques or code in action, and so on. This is not a bad thing, since happy, motivated people do better work and someone has to maintain anti-spam systems.
(I certainly often felt gleeful when I was actively maintaining local anti-spam filters. It was only when I stopped doing so for a while that the idea of doing more anti-spam work stopped feeling like fun and started feeling like a pain.)