As you did not specify the particular route you wished to follow, nor your time frame or photo interests and/or your physical capabilities, I will just throw this out:
Instead of heading through Medford, perhaps take 97 (at Weed, I think) and up through Crater Lake (should be good this time of year), then 197 to The Dalles (on the Gorge). The Dalles is a short distance to the old highway and "Waterfall Row". There are also a couple WFs on the Washington side of the Gorge as well as a couple wineries, a museum and Stonehenge type war memorial. We just did the Gorge and water is good at all falls. There are also a couple prime spots (on Wa side) to capture kite and sail boarders. There were a gazillion when we were there and you can get them backlit in the latter part of the day. Take a long lens though as my 70-200 was not quite long enough, wish I had taken my 200-500.
As I absolutely hate travelling I5 through the Seattle area, I would go through Portland, W/B and get to the coast, then take the coast road up into and through Olympic National Park. Unless you have commitments in Port Townsend, I don't find that area as interesting as the west coast of the Park, so the coast route keeps you along the coast and, if necessary, you can reach Pt Townsend via the west/north route.
Also don't know your budget/hotel/eating preferences, so won't throw out any advice in that respect, other than to say, the Gorge has a lot of hotel/motels as does ONP, a couple nice (and pricey) places which are right on the water.
Marv