I used to live in Hood River county where there's lot of good places.
Lost Lake is probably the most spectacular though.
It could be a nice ride up there too but it's a lot of climbing for a 250.
(Do you have disc brakes or drum brakes?.... just asking)
Have you considered a 400-650 dual sport for this trip?
Washington country (where I live) you might want to skip. :-)
Hagg lake is about it. Make sure you go when there's water in it.
Downtown Hillsboro is OK and there's the farmers market on summer weekends.
Maybe the air show would be something to consider.
Other than that, there's the Ron Tonkin baseball "stadium", Nike headquarters, and several Intel plants.
Not exactly a tourist destination.