For whatever this is worth, I have made that trip several times towing a small trailer. We did not cross over the line at all. But it is a twisty road, sometimes busy, and the driver will not get to do much sight-seeing.
Average speeds are substantially less than 30 mph, especially if there is local traffic making left turns. (Obviously, it is a narrow two lane road, and there are few if any left turn bays.). And some of those locals brake real fast before using the turn signal, so watch out. Don't ask how I know this.
If your destination is on Highway 1, such as the RV park at Westport or whatever, then of course you would take the coast. But if you want to get up the coast faster, take Highway 20 to the 101.
And if you want to stop and take pictures, you are much better off doing that when traveling southbound. There are pullouts with great ocean views. Not so much when heading northbound.