The ‘auto silence first post regex’ feature is a really great feature. Super useful. 
I think It would be even more robust if there was some equivalent that could be used for non first posts too.
I.e. Either an almost identical regex option that covers all posts. Or another watched words list in the ‘Logs -> Watched Words’ section. Similar to the Watched Words -> Require Approval or Flag lists.
The only main risk for collateral damage that I can think of, besides human error, would perhaps be if an innocent user quotes a post that matches the regex or watched word list. In that case though, I believe silenced users can still pm mods in order to fix it.
Although scrutinizing first posts can catch a lot or most of it, it’s quite an old forum spammer trick to first post innocent posts to help get past the initial account scrutiny i.e. in ‘introductions’ or ‘random/lounge’ sections. Another is to come back later and edit their innocent posts to include links or w/e.