I'll take economic umbrage at "don't sit with the cattle". When I traveled from Chicago to SF on the California Zephyr (40-ish hours), a seat was $100 and a sleeper car was over $1,000; for reference, a flight between the two is about $200. Being able to afford such a sleeper car is the sort of luxurious expense that most vacationers will likely prefer to spend on going to a more exotic destination by plane.

(I do recommend the California Zephyr, and second the parent's suggestion of spending the whole of it in the observation car, but skip the part of the route between Chicago and Denver; Denver and onward is where the real action's at.)