I grew up in central Washington and now live in Spokane and this would be my route there and back. I'm not sure if your trip includes kids or not, and 2 days each way isn't much time for stops so plan accordingly.
Start across the North Cascades Highway. Winthrop is a really cool little town. Once you reach the Columbia head north to Brewster and then over the top of the ridge and right down into Grand Coulee. If you haven't seen Grand Coulee Dam you need to. Take the tour, its going to eat up a lot of time, but it is worth it. You probably won't be there for the nightly laser light show on the face of the dam, but if you are its also worth it.
From Grand Coulee head to Coulee City and Dry Falls. Its out of your way, but worth a stop. If you don't know about the Lake Missoula floods google it. Dry Falls will make more sense if you know what happened. From here to Montana you will see evidence of the floods once you know what to look for.
Take Highway 2 to Spokane, mostly farm land and small towns in between. Spokane is a little big city, and CDA is a little smaller. Lakes, rivers, mountains, fun downtowns, history, museums. Frankly with your schedule I would skip over and save for another trip.
From CDA take I90 through the Silver Valley. Wallace is another fun little town. Old mining town in a steep valley that was saved from I90 by elevating the freeway and building it into the side of a mountain. Wallace being a mining town was full of brothels in the day with the last one closing in the late 80s. The museum is interesting.
From Wallace stay in I90 until you get to St. Regis. The big gas station has the best huckleberry milkshakes, and a cool fish aquarium in the back. Across the street is an antique store that sells great beef jerky. 20 minutes and you are back on the road headed to Kalispell.
Kalispell is another cool town, but the one stop you must make is Moose's Saloon. Great pizza, and you can carve your name into the wood walls.
White Fish is another small town that's cool, but the out of town money crowd has found it, and it has changed accordingly.
Enjoy your time at Glacier. Its definately worth the drive. The one thing you have to do is the Going to the Sun Road.
On your way back stay to the north and travel to Sandpoint and then back to CDA/Spokane. Get on I90 and drive until you get to Quincy, and then take the road to Wenatchee. At that point you are back on Highway 2, and can drive over Stevens Pass, and back to Seattle. You can take Highway 2 from Spokane, but you will back track a little. You could always stop at Dry Falls on the way back if you take this route, but I think it would be better to go on the way there. Leavenworth is on the way along with many other small towns.
Honestly you could spend all 11 days just driving to cool places along the way, and that would cover only northern Washington, Idaho, and Montana. There are so many good 2 lane roads, and you are going to see everything from high mountain passes to desert. Another option would be to do the route I gave you in reverse. Get to Glacier as fast as you can. You may find you don't need to spend all 7 days there. Then you would have more time on your way home to explore.