How about new member automatically get their name posted to a list and existign members message them directly by way of a personal welcome?
When registering, have an option to allow new members to accept welcome mails.
This would provide immediate value to the new registrant, a feeling of community would be fostered throughout, and the likelihood of increased membership would be significantly increased.
I know that we have the the forum to introduce ourselves, but this would increase the introductions by also having this in place.
eg Fred Bloggs registers. In the forum the list is updated to show us all that Fred is new. We all have the facility to leave a private message welcoming them. Fred is over the moon at this and immediately feels like he has joined a forum with a difference (which it is). He them posted on the forum himself to introduce himself to the public.
Making this an opt in/opt out would negate the worry of intrusion/spamming.
Just an idea but it would also change the ratio of members to forum posters, enhancing the experience for everyone.