When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue. This will greatly reduce spam.
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/archives/2005/02/02/wordpress-plugin-auto-moderate-comments/" title="Auto Moderate Comments" rel="nofollow ugc">Auto Moderate Comments</a>

Ozh' Auto Moderate Comments

When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue.

The lazy and the productive will love it : all admin links available in a neat horizontal CSS driven drop down menu. No need to click on “Manage” then “Pages” to edit pages. And plenty more space on your screen.
For documentation, examples and screenshots, please refer to the official plugin page for <a href="http://planetozh.com/blog/my-projects/wordpress-admin-menu-drop-down-css/" title="Admin Drop Down Menu" rel="nofollow ugc">Admin Drop Down Menu</a>. There is also an API for plugin coders (give your plugin its own special icon!).
<h3>Questions and Support</h3>
Plugin doc: <a href="http://planetozh.com/blog/my-projects/wordpress-admin-menu-drop-down-css/" rel="nofollow ugc">http://planetozh.com/blog/my-projects/wordpress-admin-menu-drop-down-css/</a>
On <a href="https://github.com/ozh/ozh-admin-drop-down-menu" rel="nofollow ugc">Github</a>. I don’t read WordPress support forums.

Ozh' Admin Drop Down Menu

All admin links available in a neat horizontal drop down menu. Saves lots of screen real estate!

Ozh' Auto Moderate Comments vs Ozh' Admin Drop Down Menu