I've done the entire Capitol Limited both ways in coach, a one-night trip, every trip the long-haul coach full. I travel solo, so that means I'm seated with a mate. I'm 5'10'/160 lbs. 40-y/o man. I can get comfortable in aisle or window. In window I lean against the window. In aisle, I put the leg rest up, seat all the way back, fold the pillow over, and rest my head/shoulders on the arm rest. It's comfortable enough if I get situated *just* right. Major annoyances are: children running up and down the aisles. (I would have done this as a child, too, and now I can understand why my parents were always telling us not to run in and out of the house.) Passengers talking late into the night while other passengers are trying to sleep. Most annoying of all, however, is knowing the while the long-haul car is full, the short care is probably only 1/2 to 2/3 full and all those short-haul passengers travelling solo probably have BOTH seats to sleep in, which is absolutely the best way to travel in coach.
I've done the Cap and the Cardinal more times than I can count over the past decade, most of the time all the way from WAS to CHI and back. It's always a one-night trip. The only really long trip I've taken on Amtrak was in 1995, the air/rail deal. I went from RVR to St. Petersburg, FL, stayed two nights. From there to Austin, stayed one night, then on to Tucson. I recall being able to move around in coach and find and empty pair of seats. Once coach had a section in back for smokers. I sat there, being a smoker at the time.
Oh, yeah: One thing on the Cap I've been noticing over the past few years is that the coach attendants have gotten a lot more strict about coach passengers moving from car to another, or even just changing seats. I use to do it all the time back the day, especially slipping out of my assigned seat between Toledo and PGH.
I never travel in the sleeping car because all my trips are on short notice, and I just can't justify spending $200-$300 on one night of travel. I know the low bucket is $125, but I can never plan that far ahead.
One day, though, I do hope to plan a long-distance trip on one of the western trains. I think I would travel the first night in coach, then upgrade to sleeper for the second night.