This has been oft-repeated conventional wisdom from years, but I think we're giving most spammers way too much credit.

I run several mail servers, and addresses that have not existed for well over a decade, and always give 5XX responses, still get spam.

As long as spam is profitable, because it pushes all negative externalities off to someone else, it is not worth a spammer's time to cull their lists.

I simply do not see this happening.