Despite being a believer of "WordPress *IS* a CMS", I'm voting "no".

I think labeling it as a CMS will make all the noobs thinking there's a difference between "blog" and "cms" come and ask for what they think are CMS features, ie what other stuff like Joomla or Drupal make out of the box (most people think "CMS" = "better community management with user profiles", "blocks" as in Drupal terminology, etc)

Plus, I always vote against change :)