Yeah, you could go either way, it is more of whether right now is the issue of time, money, and strategy vs. long term in all of those. I would do the three, because getting more targetted will help you find customers easier and speak only to what they need.

From an SEO benefit, I would disagree that a single site is better since you would be pouring all that into a less focused site and the incoming traffic would also be varied by source and topics. I think it would be better to rank a site surrounding one specific topic and the end user will find it more useful.

Also you can leverage each individual asset to help the others and promote them where needed. From a social growth side it is better as well for various reasons.