Closing and archiving is a much better alternative to deleting. As OHMomof2 alluded to, every thread is an open doorway to the site via Google Search results…not to mention having more content indexed by Google is a good thing. Just wish Google would decide to feature fresher content in their results sometimes. I get results from several years ago even on technology-related issues that I search for…and this happens with just about any site that has aged content.
For now, I will echo what MaineLonghorn mentions about reporting old threads that you feel should be closed. We’ll look into the possibility of archiving by year or some other method for making things a bit more streamlined.