<p>I'm a bit mixed on this.  In general, I think it is better to close such questions, but some questions could legitimately be grandfathered.  I'm not sure I can articulate where I perceive the borderline to be or provide a coherent argument for it.  (I have voted to 'leave open' on some such older threads, if I could find them I might be able to do better here.)  I guess the gist of it would be analogous to how I sometimes vote to leave open on other threads (e.g., <a href="https://stats.stackexchange.com/q/1337/7290">jokes</a>) that don't really meet our criteria.  </p>

<p>I want to note though, that there are two other options that may mitigate the issues with off-topic old threads:  </p>

<ol>
<li>I have noticed that @whuber has sort-of-closed some old threads under a different status with a note attached that the thread is off topic, but does have continuing value.  (I'll try to find an example to link to here.)  </li>
<li>Old threads that are off topic and whose content has become incorrect / out of date do not have continuing value.  They can be not only closed, but <em>deleted</em>.  This means they will not lead future readers astray.  (To put this more bluntly&mdash;but not meaning to come across as rude&mdash;I do not see much argument in keeping open an old thread that is off topic and filled with incorrect and misleading information.)  </li>
</ol>
