I don't think you need to upgrade to UTF-8. That's used for multibyte characters such as Asian languages.
I think the copyright symbol is included in ISO-8859-1: see http://www.w3schools.com/tags/ref_entities.asp.
Are you storing the copyright symbol in the database somewhere or in the XML Publisher template? If in the database, is the stored copyright symbol correctly displayed when you SELECT it in, say, SQL Developer or TOAD?