Are you willing to rent a car? Do you like outdoorsy stuff?
I'll second kooshball about Pike Place Market -- I don't get why it's so fascinating for tourists. There are a couple of good breakfast places and then you'd be able to see it before it gets too crowded, though. The Ballard and Fremont markets are great (I think QA doesn't start until June), and I'll throw in Uwajimaya in the International District as another market option.
I also think the view from Kerry Park is better than the Space Needle, and there are no lines and it will either cost you bus fare to get up there or if you have a car then it's nothing.
My husband and I just did a kayak tour with Alki Kayak Tours which was a lot of fun and if you dodn't have a car the West Seattle Water Taxi drops you off right there. Taking the ferry over to Bainbridge island for lunch/bruch is nice and a good way to see the skyline. If you like planes and flying the Boeing factory tour in Everett is neat, and if you like baseball the Safeco Field tour is interesting and pretty cheap.
Travel is fatal to prejudice, bigotry, and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome, charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime. Mark Twain
Depending on what you want to do you can rent a car downtown for the day and that would save you parking overnight (which is quite pricey). I would definitely recommend heading out to Snoqualmie Falls, which will also put you close to the mountains.
Travel is fatal to prejudice, bigotry, and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome, charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime. Mark Twain
We just got back from an Alaskan cruise RT from Seattle. We did all the touristy stuff as I had never been before. Pike place didn't bother us, but we were only there in the morning.
I second the rec for the Chihuly Garden and Glass. It was absolutely beautiful. If you're going to do several sights, I would look into the city pass which gives you some of a discount.
Serious Pie -- yummy yummy pizza! Unusual but so so good. (and I am not that daring when it comes to my food) The yukon potato pizza was my fav! All of Tom Douglas' restaurants are great -- but I would run to Serious Pie if I go to Seattle again.
Chocolate Indulgence Tour with Savor Seattle. Insane and beyond fabulous! Awesome tour guide and super yummy tastings at several different stops. They have other tours but we all wanted chocolate!! You also get a discount card to all the places the tour -- even if it isn't on your specific tour.
Pike Place Market is great! So many things to see. We did the Ghost Tour -- not great. I would skip. The Underground Tour was HORRIBLE! Don't do it.