I think restricting new members to the new members forum (for the first post) is a good idea, it can make legit users feel more welcome as well. At least if anyone replies and says hi... I confess I'm pretty bad at visiting that forum myself
The other weapon could be a (small) delay. A captcha that requires more than one click (you know the kind I mean) and validation email delayed by 15 minutes. This would require more patience on the part of batch registrants, but wouldn't be much of a hindrance to new members.