Definitely use them, since you won't be able to upgrade until you arrive and the 'gate price' has gone up. You'll save a lot by using the passes you have.
cleo's right. All upgrades are done using the gate prices at WDW. Since they just increased, you'll be paying more for the two days you already have. And if you had bought that old pass prior to the last across-the-board ticket increase in September 2002, you'll really be getting the short end if you upgrade them now.
Dreams Unlimited Travel is committed to providing you with the very best vacation planning experience possible. Our Vacation Planners are experts and will share their honest advice to help you have a magical vacation.