Agree with the above poster that if you want to be sure to get your discounts and parking (if included on your pass), then you will need the actual card. (Don't forget that you can get AP discounts off site at certain restaurants, too -- your server will ask to see your card.) Also, if you ever go with a group that doesn't have MP and you want everyone to have the same FP return times, you will need the cards to use at the FP machines.
Here's hoping that you find your old cards!