This maybe why Theymos disabled this feature (
show stat) on the forum several weeks ago. Maybe due to burden from abundant newcomers and spammers, in particular.
Only the admin might be aware of the recent number of registrations happening per day but it really does not make sense to create multiple accounts.
This is only right with real spammers, who are actually lack of skills, knowledge, experience in the forum. They actually are not able to write even only one high-quality thread. However, I wonder alt accounts of skilled members, who are capable of manage simultaneously many alt accounts, and write good posts for each account to rank up. But, as you said, it requires a lot of time, so merit system will reduce the endemic from spammers and account-farmers.
You can level up 1-2 accounts to member level by cheating the system but this is not possible for members with 10 or more accounts.