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I'm not sure I see the motivation for people to +1 something. For Facebook, social connection is a big motivator: people want their friends to see what they 'like'. How many people actually view other Google profiles like we do Facebook? Why would anyone use the +1 in Google? I think understanding the motivation might be a key to understanding how to leverage it better.

I dont have any evidecne an old link is any better then a new link simply because it is old. A lot depends on the linking web site, if it is gaining authority and rank then your link will also gain value. But this can be the reverse.