Albertans are exempt from sales tax on tangible goods meant for use outside of the state (so things like clothing and electronics but not food/services). Also apparently on the native reserves the stores have the option of charging sales tax so if you go to the Seattle Premium Outlets you might end up paying the tax in some stores. The relevant link is:
http://apps.leg.wa.gov/rcw/default.aspx?cite=82.08.0273
If you are into music history the Experience Music Project right next to the Space Needle is alright, though as mentioned it's a lot of Hendrix and Nirvana. Shouldn't be hard to get tickets for the Mariners. I was at a game last week and it was at least half empty. If the Sounders are playing you might want to try getting tickets for that - they sell out every game but it's a fun experience.
The Boeing factory in Everett is a good tour. It's a 90 minute tour and shows the assembly building for the 747, 777 and 787. The first 787 is being delivered from there next week I believe so they'll be getting ready for that.