Multiple domains for similar content?

Which is better for managing multiple domains? Redirecting all mini websites to the main site permanently or keeping mini websites with unique content and using them as a link source to the main site?

• One of our clients owns lots of domains with such local names below: http://www.city1smallbiz.com http://www.city2smallbiz.com http://www.city3smallbiz.com They have built up all of them with one same template, however they filled them up with unique content for each. They are backlinking to the main site, with each of them with the brand keyword. I was considering 301 redirects to the main site, since they use the same template; however, I realized the content was unique and didn't risk losing the backlinks form existing mini sites with unique content. What would you suggest? Should one redirect all the websites with 301 to the main site or leave the mini sites with original content as they are?

• Answer:

  It looks like a pretty obvious private domain network that doesn't add additional value to me.  I'd be shocked if there were any unique benefits credited from any type of interlinking.  In other words, they're not really gaining much of anything, SEO-wise by doing this.  It hasn't always been this way, but Google's been smart enough to recognize these sorts of schemes, especially if they're all named so similarly, for a long time.  It's just one signal of many (getting right down to IP address, registrant contact info, design of web site, style of content writing, and so forth).  Catching these networks is a major focal point for Google.  So instead, my line of thinking here is to think about what they're losing.  Private domain networks have gotten 'penalized' recently, but I'd suspect this is "clean" enough to where that may not be so much an issue (it's not like it's a link farm for random link buyers).  But they are losing a powerful common brand, like yellowpages.com might have in a similar market.  They're probably using domain authority, when one domain gets linked to directly, and others don't.  And building up domain authority isn't easy.  Personally, I'd 301 rewrite each of these sites to a subfolder on a common domain and call it a day.