Yes, this is my go-to recommendation, especially when the weather is nice during the summer!Book brunch at the Space Needle - expensive but worth it and you get VIP access to lifts and observation deck and the food and bloody marys are great. Try a seaplane tour of the region, can be pretty bargain priced for what you get. Rent a kayak from Agua Verde and paddle around the houseboats, then have tacos and margaritas at the restaurant when you come back. Go to the Museums (Asian, modern art, pop culture etc). Go check out the Amazon biosphere building thingy. See if you can get a tour of it.
Agua Verde also has some amazing homemade biscuits if you want to get one of those early in the morning before the main restaurant opens. Good way to avoid the crowds too. So my go-to plan is to book brunch at Portage Bay Cafe in U District instead, grab a biscuit at Agua Verde before kayaking, then walk to Portage Bay from Agua Verde after.