It's about half the cost of the cheapest flight I could find to SFO from ORD. Personally, I wouldn't do it - I'm just saying greyhound seems like an even worse choice than a train.
I would seriously consider doing it for the experience / as a vacation (I like trains), but not as a serious mode of transportation.
Am I missing something, or are you able to sleep in the coach seats?
The actual beds aren't bad though, and the dining car food is decent.
At half the cost, I get it. It's not pleasant, but there are plenty of people for whom the money is a lot more important than the time. Particularly if you're not currently employed, for example.