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Having the same registration, in of itself, will not hurt SEO.  Where you may run into problems is if you are doing blackhat SEO, or doing things against Google's terms of service.  If that happens you could run the risk of your "neighborhood" getting similar punishment/treatment.  If you are doing everything correctly, or mostly correctly, then there should be no problems.

Thanks Mike! In your opinion, big 301 redirects would be totally better ?

I have spent a huge amount of time lately reading a lot of SEO information and have never seen that suggestion made. The closest would be Matt Cutts sharing how he slightly altered his page title from his H1 tag to capture an additional version of a key word.

Thank you Theo for your response, I really appreciate your time and answer.