Help Requested -- Archiving Last Year's Nings & Blogs

I'm sure this question has come up multiple times, so I apologize for the repeat but...

We are in the process of setting up our blogs and Nings for the start of school. Am I better off creating brand new URLs and sites (perhaps using graduation year in the URL) or continuing on with our old URLs & sites (which are already set up, customized, etc.)? Part of me would love to recycle the old sites, but how do I archive last year's posts? What do all of you do?

Thanks in advance,
Barbara Cohen