We love spending time at the resorts! It's one of our favorite things about visiting WDW. Sorry if some of my ideas are repeats, just writing what I can think of. For now, I'm only listing the resorts near the Magic Kingdom.
At the WL - you can get a tour of the resort, be an honorary flag family, eat at the great restaurants, rent the boats or bicycles or walk the trails. They don't have a full-service spa, but you can book a massage. Watch the water parade from the beach. Game room for the kids.
At the Poly, they usually have live music in the lobby in the evenings, you take a romantic stroll along the paths at night, or enjoy dinner/luau show. They also have crafts and hula lessons for the kids, I believe. Game room and boat rentals as well. We enjoy watching the fireworks from the beach and swinging in the hammocks.
At the GF, they have several good restaurants. Also - afternoon tea. They have live music in the lobby and nice walking paths along the beach. They have a full service spa which I've heard is nice. They have special programs for the kids, so they are supervised, while the adutls go to dinner or the spa.
The contemporary has a good game room. Also - the California Grill for dinner and fireworks is a must. Sitting in the lobby watching the monorail come through is neat. Boat rentals are available here as well.
We like looking through the shops at all of the hotels, too. Or grabbing "just dessert," since we're usually too full right after dinner. :slurp: