My first time at Disney I was 4 and remember a lot of the extras. We just had my daughter down there in January (she turned 3 in March) and she still talks about our extra activities.
We went to the Ft. Wilderness campfire program one night and our whole family (husband, mother in-law, father in-law, my daughter and a very pregnant me) loved it. They have a campfire, a sing-along and a visit by Chip & Dale then they show a Disney movie. We were lucky because the movie they were showing the night we were there was Cinderella -- my daughters favorite at the time. They also have a hayride at Ft. Wilderness that my daughter loved. There's also a petting zoo at Ft. Wilderness that your 4 year old might like. Plus, getting there is half the fun if you take the boat over from MK!
The water mice are fun! My husband and I took one out from the Downtown Disney area when we went down for our honeymoon. Not sure what the age/height restriction is on them though. Comedy Warehouse at Pleasure Island is a nice escape for adults.
Hope this helps!