We've done the park twice...it was FREEZING. You can go into Chocolate World to warm up (and hit the ride and the free chocolate at the end!).
We've never done the lights, but I've heard it's impressive.
One thing that we did in Hershey one summer was the Hershey museum...I can't for the life of me remember what it was called...Oh, the Hershey Story I think. Your kids might be a smidge to young to really get all the info, but you and your wife will enjoy it. They also have a chocolate lab where you can make your own chocolate, and a cafe that offers chocolate tastings (of melting chocolate...really interesting to do!)