I'm not sure that looping to the east really saves time or hassles. I live between Seattle and Everett. I've taken 203 etc back from I90 (e.g. to Duval, and then west to Woodenville). While generally pleasant in a car, I don't think it saved me time over 405. There are just too many stops and turns.
I've also taken 9 all the way from the Canadian border. It's nice (and they just replaced the narrow Pilchuck River bridge). But with development around Lake Stevens, 9 south of Arlington has become increasingly busy. I've seen a number of construction projects on the WSDOT website seeking to improve traffic flow along 9 and connecting roads.
I'd also hesitate sending visitors on these roads without knowing something about their navigation skills, etc. Often it's simpler to just stick with the freeway, and accept that there will be some stop and go stretches during rush hour.