You could easily spend a day walking around downtown. I would go for a Seattle City Pass, I believe $100ish per person, and it gives you tickets to the touristy stuff in the area. You can catch the light rail system from SeaTac airport to the heart of downtown for cheap. I just went to the exotic show they have every weekend in the Redmond Town Center and would recommend it too! I do believe it is every Saturday @ 9AM. Hope you have a blast!