No, it's not. Once a forum becomes more successful, there will be an incentive for spammers to adjust their algorithms so they can handle the hurdles.
In my opinion, one needs to do two things:
Create a moving target. That means for example not to let the registration and login process always look the same, so it becomes more difficult for spammers to automatize the registration and login process.
Reduce the award for the spammers. Spammers are looking for quick attention, they don't have the time to create an account and intelligent content first. So let all posts containing a link from new users be visible only to registered users or even flag them automatically, so that they never become visible to the public.
I think, there will be a demand for clever extensions in this regard.