The Museum of Flight might be of interest to you. From reading your post, I think you mean you are driving up to Everett to tour the Boeing assembly plant? The Museum of Flight is just south of Seattle by Boeing Field. I think walking or bussing to the Pike Place market for breakfast would be nice. If you go early, when it is just opening, it is not too crowded and I don't think would be as bad in September, as in the summer. Lots of good coffee shops too, besides Starbuck's which are everywhere, obviously! You might like Cherry Street Coffee, which is close to your hotel. I would second taking a ferry ride anywhere, if you have time. You could drive to Anacortes from Everett and take a day trip to the San Juans, but not sure how long a trip you are planning. There are so many great options and things to do and see! Should definitely hit Seattle Center/Space Needle and if it's warm enough, and it's working, run through the fountain!