The worst problem that you have is that people are set in their ways. They go to a certain forum (like DNF or NamePros) and that is it. I doubt that you would have a lot of success putting up a new domain forum even if you did one on 'DomainNames.com'. I put up a real site that took a lot of time and for which I am interested and have knowledge. The existing competitive site is a forum with a classifieds section imbedded in the forum. It is sitting on a site that is otherwise largely non-functional. It is where people with this interest go though and short of shutting down I doubt that anything will kill it. They did even do that for three days and got 606 registrations on the 3 day temporary forum! My 'pretty' classifieds page with lots of other info and an unused forum gets traffic but almost no posts. Its like trying to set up an alternative auction site to ebay. People are afraid to list anywhere else plus it is just where they go. The net is one big global community and most of the sectors are well staked out now short of finding something new like YouTube or Groupon or, maybe, very local - my next attempt to be!
My suggestion to anyone is not to buy forum software as, A - your forum probably isn't going to work (sorry but true even though I am still trying!) and, B - there are a lot of good free programs. My latest attempt is using Simple Machines (
http://www.SimpleMachines.org). That software seems to come very close to vBulletin and its free! Should you be lucky or have managed to find a niche, you can still buy VB later and move your database to VB. I gather that isn't hard (haha).
For an example of the SMF forum look at
http://www.AntiqueRadio.net which I built to replace the on site Phorum Forum. Phorum is another free program and if you are a PHP programmer it may have value. SMF has more support though and there is lot more that you can do with it with modest knowledge. phpBB and myBB are the other big free forum programs. I am hoping that linking it to my site AND giving it a very good independent domain name will help perhaps in both directions. I have my doubts but hope springs eternal!
BTW - The domain that I am using for the primary site is a mainstream one for my topic,
http://www.VintageRadio.com (and I PAID for it!). One other lesson here is that even a great domain can't change habits even if it does draw some traffic.