By observing the behavior of Google’s spam filters (what lands in the spam folder and what doesn’t) you can clearly see that Google is not doing an effective job at applying generally to all users what it learns is deemed spam by some other users. Otherwise it wouldn’t flag its own Google News Alerts emails for example and many other legitimate emails as spam. So your efforts might not be having as great an effect as you think. But it should affect your own mailboxes at least, and maybe that’s enough.