If that be your plan, yes 38 is a great drive. Don't forget to stop outside of Reedsport at the elk viewing area. Personally I would forgoe I5 and just drive the entire coast. Just too much to see to miss any of it.
If the weather is cooperating, while at Winchester bay get one of the dune tours. There is a pretty good sea food place on the pier just across the boat basin from the park. Next stop north should be Netarts Bay rv park. A few miles west of Tillamook and right on the bay. The front section is older but offers fantastic views. The back section is pretty new and has 50 amp service, but no views. From here you can explore Tillamook, the cheese factory and don't forget the historic museum and wonderful mural painted in the 50's by Lucia Wiley. A rather famous muralist who did quite a few public buildings. Astoria is also full of history. And don't forget fish and chips at the Bowpicker.