I live in Delray Beach, FL
- but I've visited SEA
many times. I've driven around the northern perimeter of the airport and found a great area right under the approach when flights are coming in from the north. This was the only place I found that I could get decent shots other than when I got off of my flight and took photos from within the terminal. If you get a chance, PDX
is wonderful for spotting from the parking garage.
Also, I do not know about the museum at Boeing Field - but a trip to Everett is well worth the trip if they still offer a tour!
Have a fantastic trip - I am envious, as I love travelling to Washington state as often as I can.