I rode the EB roundtrip 2 years ago. When I made my reservation, I requested a roomette on the RIGHT side of the train going WEST (aka the engineers side, the north side of the train) and I requested the LEFT side coming back (with the same views as my first part). I chose this side after exhaustive research. I wanted to see more mountainous views and views of Puget Sound. I DID get what I requested. Yes there is a chance that you may not get the roomette you ask for BUT its worth asking for.
Other than mealtime I spent most of my time in my roomette. Why? I have many reasons some are: comfort; its quieter than the "public spaces"; you can eat snacks and drink beer with no "vultures" circling and looking at your food; when its dark you can close the curtain to the roomette and turn out the lights and after the eye adjusts its amazing what you can see; the roomette across from me was vacant so I was able to move from side to side if I chose to do so (I asked attendant before doing so and then followed up with a nice tip); no people to block your photos; when tired all I had to was to close the door and nap- little effort needed; Sightseer Lounge can get filled quickly, leaving little room to move and with ruined photos. I also chose to sit along the window at mealtime, amazing what you are able to see from that vantage point. I could go on but you get the idea. Take sometime to check out the train. I did ride the rear through the entire length of the Cascade Tunnel. Take time to get to know your neighbors they might let you sit in their roomette if its on the opposite side. Ask your car attendant for any suggestions for specific sights and where you should be to see it. Due to the amount of the tip I gave my car attendant, I was given extra consideration and treated accordingly.
Do your research BEFORE you leave for your trip. Don't burden yourself with this ON the train, it makes it less enjoyable. When you get on the train, sit back and enjoy the ride and the scenery. Don't worry if the train is late- this just gives you more time to enjoy the scenery and your surroundings. I hope this has helped.