I think there should be a feature that lets moderators/admins move multiple topics in one board to another board... have check boxes next to the topic and a button to move the selected topics and then choose the board the topics should be moved to. Just an idea.
User CP -> Profile -> Look & Layout Preferences -> Show quick-moderation on message index as checkboxes
;D
Mass moving topics works well with my Move Old Topics mod.
Be careful when doing this, any mistakes and you could move all posts to 1 board.
Just set it to 0 days and select the board you want posts to be moved from, then select the destination board.