I agree with Adam. I would like to add a couple of points, from experience.

I love a hybrid approach to this. I create a central hub (just like Adam suggested), and cross link my satellite sites. This has GREAT SEO implications because you are building in backlinking. However, from experience: make sure that you clearly have a link between the hub and all satellite sites. For example, many internet marketers will focus on very diverse niche's. If you have a site dedicated to a children's product and you cross link to a site dedicated to dating advice, you are likely to get penalized by google. They will match your backlinks for related content and have some pretty complex formulas. My rule of thumb, if you can look at a link and determine that it does not relate to the page that it is on, or it conflicts entirely with it, so can their indexing formulas.

~ Delana