Are you sure a subforum would produce more attention? I kinda agree with what Donald said re: the board games forum:
Posting begets posting. I think it's better to have forums broad enough to fill up a screen with active threads; when it exceeds that, split it up into two forums. The exception is when you want to be able to hide/ignore a forum.
So, I wouldn't split off video games; it just means forums with fewer active threads. Combining video games and board games is the correct direction, except it's moot at the moment since general discussion doesn't get that much activity either.
If you make a subforum, you'll get less "incidental" traffic from folks who might see it in the forums they already frequent. I think there's plenty of room in the general Dominion forum for kingdom-design threads, and if you guys ever get so noisy nobody else can put up with you,
then it's time for a subforum. I guess my point is, if you think there should be more discussion of kingdom design...start discussing some kingdom design! You don't need theory's permission via a new child board, and I don't think getting that permission would create any particularly long-lasting motivation to keep discussing them anyway.