Hi Smiten and welcome to the DIS! By all means take along those old tickets, since at the very least you'll be able to apply them towards the purchase of new tickets. However, if they're multi day tickets, you'll probably be able to use them as is, but only in the theme parks that were in existence when you first purchased the tickets. So, if they pre-date MGM, for example, you'd be able to use them at MK and Epcot only. It's possible they'd have to re-issue those old tickets so they can be used for fastpass.
Have fun!