I think your time would be much better spent at the Museum of Flight at Boeing Field (BFI), which is only 15 minutes from SEA via I-5, and you don't have to travel through the city. I was planning on doing the Everett tour this summer, but I had heard that it was rather underwhelming with only ~15 minutes on the factory floor, and so I opted to do the museum instead. The displays and airplanes are amazing, and the place is huge. I spent over 6 hours in there and didn't get to see everything. Plus you can go into an old Air Force One 707, a 787, and a Concorde, and BFI is an active airport, so there's always planes moving in and out.