Yeah, I agree that the tough spots on Walker are the two big "dips" that culminate in narrow bridges over creek crossings with no bike lanes: Between 173rd & 185th, and then again between 185th and Amberglen.
If you're looking to have a more consistent bike lane or shoulder, you have a couple options:
1) When heading W on Walker, where it narrows down and the bike lane crosses over the right turn lane and then ends: Turn Right there onto 170th. Follow 170th up to 173rd and then take 173rd to Cornell & take Cornell to Amberglen. 173rd doesn't have a bike lane, but it has a little less traffic & a slower speed. That first stretch of Cornell is just finishing up a big widening project, so it was a mess all summer, but they've finished widening and paving it now. As of last week, they hadn't painted the bike lane stripes yet, but that should be done pretty soon. Just watch for people crossing the bike lane to turn right onto Evergreen.
2) ride through the first dip, and then turn right onto 185th and take that to Cornell. getting over into the left turn lane on 185th can be tough, so you can just do a box turn in the crosswalks to avoid that. this is a little less out-of-the way than the first option if you don't mind the section of walker between 173rd and 185th.
But personally, I just prefer staying on walker because it's more direct. I just take the lane fairly early once I'm on those downhill sections approaching the narrow bridges.
I suppose I've also ridden the route enough times in the daylight to always know where the shoulder is going to end.
It sure would be nice if they would put wider bridges in at those creek crossings so that we could have bike lanes.
My only other complaint with the Walker/Park route is probably my biggest concern: When travelling eastbound on Walker, getting out into traffic to make the Left turn onto Park (with no turn lane) can be sketchy.