I'm thinking of making Games & Rounds not count toward posts or activity.
For the love of god, yes.
They are going to stay in the "last posts" list though, right?
Off topic and archival boards can probably be excluded.
Dunno about archival. I mean, just because a thread gets moved there after losing its relevance doesn't mean the posts are not worth giving activity.
You would risk someone losing posts/activity for a great/good post, because the thread has been moved to archival.
Why? It would be 14 times the number of activity periods an account has posted in, excluding those periods it only posted in Games&Rounds (or other excluded boards).
That won't be too hard to change calculators to, seeing that some like bctaccountpricer already give you detailed overviews of the boards someone posts in.