I would recommend not coming to Seattle at all. Especially not this time of year.
That said, if you insist on visiting this swamp, and you want sushi, go to Wasabi Bistro downtown -
http://www.yelp.com/biz/wasabi-bistro-seattle-3
If you're looking to get your money's worth for the Space Needle, the best thing to do is get the double deal. Don't eat at the restaurant - its not BAD food, but its way overpriced. The cost of going up once is kinda expensive, but getting a twice-in-a-day ticket is only a couple of bucks more, and you can get the trip both day and night, which is kinda cool.
Personally, I find Pike Place Market vastly overrated, its just not that interesting to me. If you're interested in history, perhaps check out the Underground Tour:
http://www.undergroundtour.com/
My favorite bar, which doubles as edible pub fare and a good place to watch sports, is Buckley's:
http://www.yelp.com/biz/buckleys-in-belltown-seattle-3
Ahhh....I dunno. That's all I've got off the top of my head. Since I grew up on the other side of the country, everyone that wants to visit does tourist stuff, so I've done just about every tourist activity imaginable (which is often not the case for born-and-raised locals, for example I've never been to half of the historical destinations in Philly), so if you have any questions, ask away...