-焰火two places to view: Gasworks park (overlook Lake Union, and downtown skyline) and Elliott Bay waterfront.
-Snoqualmie Falls: don't think it's worth going (but again that's a personal opinion - I have seen too many waterfalls). Big Four Ice Caves on Mountain Loop Hwy is more interesting. Should be able to get a whole valley of waterfalls if you are willing to do an easy flat 1 mile hike (without the hike, the view is just as beautiful).
-去 St. Helens, 住Olympia: personally not a big fan of St Helens. It's only more interesting when steam is coming out. North Cascade NP is better.
-去Olympic National Park: there is no tropics and where does 热带雨林 come from? It is one of the 3 temporate rain forests in the world. And it's the rainiest area in the whole country. So there may not be 阳光海岸. Regardless, Olympic National Park is the most interesting NP in the country. As the previous post says, don't miss the Olympic coast. Ruby beach, Riato Beach, 1st, 2nd, and 3rd beaches - all heavenly beautiful. Stop by Dungness Spit if you have time.
7/10 Stanley Park, English Bay, Grouse Mountain. Chinatown. I would also drive at least to Squamish (on the way to Whistler) on the Sea-to-Sky Hwy. Skip Chinatown and go to Richmond instead unless you visit China for its history.
-温哥华half day, 下午回西雅图, 晚上的飞机.
On your drive back to Seattle, be sure to visit Artist Point at the end of Hwy 542 in the Mt Baker area. It's a long drive and would be easier to get to if you enter US via Surrey (I believe that's the name). Mt Shuksan reflected in Picture Lake is the most photographed view for a good reason. Weather permitting, you might also see Mt Baker at Artist Point.
-Another good stopping point (perhaps not to be missed either): Deception Pass off Hwy 20-You can visit Deception Pass State Park and the bridge.
Visit Washington Park in the town of Anacortes and watch sunset over San Juan Islands on top of Mt Erie .
-Time permitting, Orcas Island in the San Juan Islands is a great place to visit.
Don't know why everyone is skipping Seattle/Western WA for Vancouver. You can easily spend 2 weeks just in the Seattle vicinity.
Enjoy your trip and be sure to check weather/road conditions before heading out.