Going with a specialized board is a good idea, but it does run the risk of remaining unknown. How many know that there's a Galaxy Angel board (http://angel-tai.com/waka/wakaba.html) or a Vita board (http://vita.orzorzorz.org/imgboard/futaba.php)? You have to remind people every now and then without getting run off as a spammer.

One option of course is to add your specialized board(s) to iiChan's collective but there are a few rules to follow and it might not be as gratifying as succeeding independently. Though success is relative, if you get one post a day you're already doing better than some boards on iiChan.