http://riwong.smugmug.com/Travel/Seattle/525583_NxzZY#P-2-10Link to my Seattle Gallery.
The only game in town this year is Lk union
Since the lake is located in the middle of the city you have a view from just about any where you see the lake. The above shot was taken from the south end of the lake looking north. The fireworks are fired off a barge in the lake so if you want a front row seat you need to be in a boat.
Take a look on Google earth and center in on Lk union and decide where you want to be. There are hotels that have a view of the lake. If you do head into the area the traffic will be bad. some people spend the day to get their spots. The trick to get good firework shots is not to use auto and set the exposure manually for the display and not the sky or forground. if you are seeing lots of smoke it's because you are over exposing your picture.
Because it does not get dark up here till 10pm if you are driving into town you might not get home till way after midnight because of the traffic. most streets around the lake are just two lane city streets and everyone will be leaving at the same time.
As for city shots the iconic Seattle shot is taken at Kerry Park just north of Seattle Center.
If you plan to see the sights Seattle is part of the CityPass program.
http://www.citypass.com/seattleThere are sites like the space needle and the harbor cruise which will allow you to get shots of the city that you can do no other way. Also if you just want to get away to shoot drop the family off at the zoo and go shooting nearby.
if you want to shoot nature in the city the Seattle Arboretum Wetlands are right by the UW campus. near the zoo.
http://riwong.smugmug.com/Nature/Seattle-Arboretum-Wetlands/2163366_f9iqi#P-1-10At the UW boat house you can rent row boats or canoes by the hour.
If you stay in the downtown core you can get around the city core for free during the day because the buses have a free ride zone in the city downtown area.
There is also a light rail into the downtown core from the airport for $2.50 per person.