Unless you pay for an upgrade, you only get 2 DBs.
As an alternative, most scripts (WordPress, Joomla, etc) allow you to add a prefix to the table names so the same DB can serve multiple scripts.
ie, descalzo_blog as a database could hold a set of WordPress tables with a wp1_ prefix, Joomla tables with joom1_ prefix, and another WordPress installation with wp2_ prefix.