If you don't like the seat you're assigned, maybe the sun is in your eyes or your seat is positioned backwards to the forward motion of the train (a pet peeve of mine), just get up quickly and choose another one. If another traveler comes by to claim it, well so what? Just smile and move on.
After all, you're a traveling Pauper and we have to do what we have to do, to be comfortable.
Trains are a great way to travel. I don't personally like to spend overnight on them, however. In fact, I don't like to ride on them for longer than 4-5 hours. That's enough for me. I plan my itinerary around this preference. You can do the same, if you choose. I always find a place to stay, usually a hostel, at a stop along the way and catch another train or form of transport the very next afternoon (giving myself time in the morning and early afternoon to SEE some of the features of the place I stopped at).
You can't beat the slow pace of a train as you connect with an earlier era. There's something nostalgic about train travel, magical in its own way.