Besides the Tulips, there is a major road repair happening between Everett and Marysville. I understand that lanes are shifted and narrowed so they can replace expansion joints. You could safety take the detour you suggest, the roads are good, but I doubt it will save you a huge amount of time.
We take 529 (old highway 99) occasionally to bypass that stretch of I5 but everyone else is probably taking it as well. I think the bridges have adequate clearance because large trucks go that way but I haven't paid any attention lately and have not gone that way with our MH.