I was thinking that the low influx of new people must be because account registration is locked down thanks to the spambots so much. I know of at least one case where someone emailed me about having issues of not being able to register.

So I was thinking... How about allowing new accounts to post again, and lock down their account/send them a message/delete the post automatically once their first post on the forum contains any links?

There are also spambots that post text, with some keyword words to increase the rating on Google of these words... but the idea is sound. Maybe also allow one single post the first day?

That could work too. If at all feasible, then any kind of spam detection on the first post would delete the post/put it in quarantine and block the account.