Hi there!
This has happened to my husband and me. See, we both worked at WDW during college, honeymooned at WDW, and have been every year since we were married in 2000 (and we live in MA now). When we were set to go last year with a week left before travel, we found we were missing the usual excitement.
So once we arrived, we challenged ourselves to find the "hidden gems" of WDW. To us, it's not always about the theme parks but about the atmosphere; we can leave our back-home worries behind. While we were staying at Pop Century (a new experience for us), we visited Coronado Springs, Polynesian, and the Contemporary (all resorts we had not yet had a chance to really see) and just strolled about the grounds and visted the shops. It honestly was one of the nicest days we have spent at WDW (and it was raining to boot).
Sometimes we make sure we try a new restaurant (I think someone once told me there are over 200, so we have a ways to go before trying them all). I finally tried the famed Tonga toast and this, too, was a fun experience.
When we went to EPCOT, we made sure to really look around each country's pavillion and chat with the CM's. We discovered the beauty of Morocco and learned how the artisans created the beautiful tile mosaics. We went to the Stave Church in Norway (quite interesting) and walked along the "forest" in Canada.
I hope you have a magical trip!