Hwy 2 is quite scenic. Right before you hit Leavenworth, you might stop by roadside and see if there might be spawning salmon in the river by the roadside (august might be too early for that). In fall, the river turns red with migrating salmon.
Once you pass Bavarian town Leavenworth, you enter the orchards of Wenatchee/Chelan with rolling hills of apple/fruit orcharids. It's much drier and very hot in summer. I suppose you will also hit the Western themed town Winthrop (looks like the scenery of Western cowboy movies) and then come back out on Hwy 20.
I guess you might be OK coming up on 405 from Renton since you can carpool. But I have often seen the carpool lanes get highly congested as well.
I was kidding when I said cherry picking in Aug (I know there is no cherry picking in Aug) and it's probably too early for apples.