I see plenty of opportunities for targeted advertising on 4chan. Obviously, it's hard to have targeted advertising on the larger boards for subjects like "random" and "video games," but you can make pretty safe assumptions about the demographics for other smaller hobby-centric boards; the cosplay & EGL board is mostly populated with young women who are into dressing up and going to conventions, the "traditional gaming" board is mostly (young) adult males who are into tabletop games like D&D and Warhammer 40k or trading card games like Magic: The Gathering.

I mention these two boards specifically because I think that they represent valuable demographics. The cosplay & EGL board of 4chan is where people go to talk about the dress that they just spent $300 on (and that's on the low end--for some of those girls, $300 is what they'll spend on cosmetics seasonally). By the same token, tabletop games and trading card games can be big cash sinks, and there are plenty examples of people who spend hundreds of dollars per month on these hobbies.