Hmm, interesting. If I buy a two-day ticket (not the three-day CA one) for August 14 and 21, would I then be able to upgrade from those to a new Dream Key and merely pay the difference (about $1,200)?
No, because you have to upgrade before the end of the second day you use the ticket and the new passes don't go on sale until the 25th. You cannot upgrade a wholly used ticket.