Assuming that the train isn't running late, the prime scenery you'd be missing by getting off in Oregon is Mount Rainier. If you've never seen a glacier-clad volcano, it's something to behold. The other consideration is, if you are a restored train station buff, both the Portland and Seattle stations are gorgeous, and very different architecturally. If you stay on till Seattle, the stop in Portland is long enough to give plenty of time to admire the station there, inside and outside. It's a classic! King Street Station in Seattle is, along with Los Angeles Union Station, tied for my favorite West Coast Amtrak station from an architectural point of view. It's absolutely unique in its stunning restoration. And, right next door to King Street Station is the old Union Station, which has been renovated as an event center but keeping all the nostalgic train signage intact. I'm not sure if you can still wander in or not; as of two years ago, the front doors were generally open and they didn't mind folks strolling in to take pictures. Of course, lots of things are different from what they were in the Before Times, so perhaps that isn't possible anymore.