Archiving annual festival site

Personally.

I would archive the 2010/etc sites to Pure HTML.

This plugin would do the job http://wordpress.org/extend/plugins/static-html-output-plugin/

This WordPress codex post describes another method. With using WordPress in its own Sub Directory and archiving sites: http://codex.wordpress.org/Giving_WordPress_Its_Own_Directory#Pointing_your_home_site.27s_URL_to_a_subdirectory