I agree. At home I know about the roads - width of shoulder, amount of traffic, etc. - and I chose my routes accordingly. On a tour I either look at a road map or use some sort of guide. This is one reason I like Adventure Cycling Maps. Their routes take you on nice roads whenever possible. They're not perfect - I've had some days when I strongly questioned their choice. I've also had some times when I missed one of their turns and ended up on a busy highway with no shoulder (my error - I should have paid more attention to mileage for turns. You have to do a little math, because their mileages are from their matchlines, not from the campground where you start your ride in the morning. On my last tour I was more diligent and didn't miss a turn.)

I had good luck, twice, following the route outlined in "Bicycling the Pacific Coast" by Kirkendall/Spring. Granted, it's mostly on Highway 101 and Highway 1, but there were a few places where it took us off the highway onto bucolic backroads - nice.

There are lots of touring books that have routes outlined. I've only used a couple.