Spam has been definitely reduced dramatically.
However, if someone can give me data points per month, I can draw a time series plot for total intra-month posts of the forum.
I actually did it, but from arbitrarily data dumps by @theymos, and forum available data (but it stopped update since last year).

From forum data update:

From theymos' arbitrary data dump weeks ago:
Total new accounts dropped deeply, I am not sure about total new posts made.