I'd say about 50% of the content on my blog is timeless - certainly the photographs are. I did have comments closed after about six months following advice I received from elsewhere. However, I had the same problem as previous commenters where legitimate readers complained because they were unable to leave replies on older material, so I reopened them. That has only resulted in a doubling of spam posts, but Akismet seems to be very efficient at identifying them, so its not a major chore to clear out the spam queue from time to time.