Regarding the value of older posts, this is something I sometimes do...

If I find a post that I like, and it is older than 30 days, I go to the person's blog and read posts they may have from the last 30 days and possibly up vote them. In fact, if I find their newer content to be something I am on the fence about up voting, I will up vote one anyway since I wasn't able to up vote their older post.

So older posts could still draw new readers who then go on to vote for newer posts.