I completely understand why this is being introduced but, new posts aside, I also see that you have a constant stream of bots registering and not posting but just updating information on the profile page such as under signatures. (See attached screenshots). If the bots can't post then the next thing will be spam visitor messaging.
On the XVBT iNet sister forum we disabled the whole Friends / Visitor Messaging / Albums thing because we felt that these features didn't really fit on a programming forum (they would be more for social forums using the software) so they were just causing a lot more trouble than they were worth. (Yes, the bots were spamming members via the visitor messaging and it was very hard to proactively moderate). Additionally, members can only have signatures once they have a certain number of posts.
If you think the above ideas would suit this forum then they might be worth a shot?