Bulletin boards that users feel are more active are more actively visited, and improve site visibility/traffic. Try condensing some boards to create a more 'real time' feel for the site instead of a 'fap then leave for 3 months until more content appears' setting.
My personal recommendation is to combine /34/, /y/, /h/, under a 'plain' hentai, put everything else into 'alternative', keep gore for itself, and split /do/ and /cm/ between these, adjust the rules accordingly. The only real question about this move is if you want a separate /fur/ board. I say just put it in /d/ and play it by ear, it's been increasingly accepted on other chans. I can say there is some market for a /fur/ board, but you'd be competing with some stiff players.
/di/ + /cd/ = /dig/ or something. Separating the two is like splitting hairs. The fetish drives, the contents themselves, are almost identical.
/fat/, while of considerable post mass, the third page dates back to July 2012 and the topic could be rolled into /fet/ if not /s/ with little consequence. Maybe staple a thread as a consideration.
Combine /ni/ and /asi/ into /ethnic/ allow latina content.
Combine /gay/ with /men/, /le/ with /s/. Why have separate boards when the only difference is the quantity of the sexual organ in question? Gays are all over the /men/ anyway, and it's pretty rare for people to object to lesbian mixed in with their female only porn, and the culture here seems tolerant enough.
/an/ is a redundant appendage, remove, permit anal content per board topic which happens anyway.
Create /health/ (for biological things relating to sex, STDs, safe sex) and/or /kilk/ or /tanky/ (Ki-nky ta-lk) kinky discussion, contemplation, advice, etc. FANTASTIC PR, helps make the site a one stop for kinky things, provides a more social depth, but separate for the sake of the 'fap and go' crowd. You can probably get away with just /tanky/, but having a separate sex/general health board has advantages ad-wise.
A hypnosis board. I saw the other thread, just trust me on this, I'm an 'professional', if you build it they will cum once word gets around. Just try it out for a few weeks you can always delete it. It would also potentially provide a springboard for considerable advertising; the sale of hypnosis files and such has been doing Post too long. Click here to view the full text.