Yes, there is a free shuttle between Qwest and Lake Union boats afloat. Very convenient. There is a street car that stops near the hotel that goes lots of places downtown, if events are held in that area. Fairly reasonable costs.
You could look at Edmonds for a hotel- the Seattle Sounder light rail system stops in Edmonds (although I don't know what a weekend schedule would look like) and stops at the King St. station, right by Qwest, and then the free shuttle could be taken to boats afloat on Lake Union.
Also, I think there is a Seattle Sounder route that goes to and from the airport to downtown. That could potentially replace a shuttle. I'd have to research to know exactly, but I've see a light rail train come from the direction of the airport a month or so ago when I was up in the Seattle are driving on I5.
I hope I can make it up from Portland for this gathering this year. In the past several years, we've always had plans on that weekend, so we've done the boat show the second weekend.
Erin