Have you considered that member profiles may be a sources of traffic? If your forum is the sort of forum where many use their real name (especially the case in some specialist niche or industry specific forums) or a name that they are well known by, then this is a potential source of traffic. If someone is using a search engine to look for more about someone who is a member of your forum, then they obviously have an interest in your niche. Make sure the search engines can crawl your profiles.
I have many prominent high profile members who used their full name on one of my specialist forums. I used Linkvana to get a enough deep links to these profiles to have them ranking in the top 10 for that person’s name. I simply write blog posts about them and their contributions and this gets distributed through the Linkvana network.
Also, make sure that your robots.txt file is not blocking the search engines from crawling the members profile pages.
The downside of using profiles as a source of traffic and having profiles indexed in search engines is that profile spam is on the increase.