I'm thinking of making Games & Rounds not count toward posts or activity. What other boards would be good candidates for this? Maybe Off-topic, though some decent discussions occur there, so I'm not sure about that.
It depends on the motivation behind the thinking for excluding certain boards.
This is a Bitcoin forum, advanced ranks based on activity should indicate that member's involvement in bitcoin.
There are posters of hero and legendary rank whose posting history is almost entirely off topic.
If activity was related to core coin subject input only i.e. excluding Off topic, Politics and Society and even Meta then any migration of spammers for sig or farming purposes to the "main reason for being here" boards could be dealt with as normal by the mods.
Some thought could also be put into the proliferation of 'opinion' threads which repeat the same theme time and again, "Is cloudmining etc etc", "Is bitcoin going up?" which are spammers' heaven.
That's if you accept that traffic falling is a price worth paying for credibility.