Should old messages on the message board be purged?

Since the reopenning of our message board I have been considering removing some of the old messages. In part this is to allow users to find interesting/relevant information more quickly. But before I start a wholesale cleanout of the boards, I would like to know what you think about the criteria that should be used or if it should even be done at all. Note, you can select multiple options.

(You can select more than one option)