The notion that domain registration length matters as an SEO factor is a myth. When asked about domain registration length, Google's Matt Cutts said, "To the best of my knowledge, no search engine has ever confirmed that they use length of registration as a factor in scoring. If a company is asserting that as a fact, that would be troubling. The primary reason to renew a domain would be if it's your main domain, you plan to keep it for a while, or you'd prefer the convenience of renewing so that you don't need to stress about your domain expiring."