I'm not sure that a board like this lends itself to much further growth in real terms mainly because it's such a relatively small audience.
However if the owners had a 3yr, 5yr and 10yr plan for the site, they would probably have similar goals as other boards in having more members sign up and contribute more threads/posts, thus generating more traffic and page views which leads to greater advertising revenue.
However if it did grow exponentially, i think i'd do the following:
1) migrate to
http://www.invisionpower.com/ away from vBulletin because it seems much more functional.
2) start allowing advertising. After awhile you don't even notice it and people can opt out of viewing ads and support the board through subscribtion.
3) get a few more moderators on to mix it up a bit more (the current ones are good but i think some have been here too long).
4) create a level 2 for 'trusted members' where we can smirk about the plebs on level 1 (kidding).
5) create a sub forum for shares and managed funds.
6) allow greater freedom of speech in the coffee lounge -- this place should be virtually anything goes as long as it's not racist, threatening or libelous.