I"m very confused about this thread. In late February I bought a saver fare ticket on the Southwest Chief. About 2 weeks later the roomette fare came down 4 days before boarding date. I called Amtrak and asked if I could upgrade to the roomette and how much it would cost; the difference was exactly the difference between what I had paid and the cost of the roomette at low bucket price. I thanked the agent for the information, hung up and reconsidered my options. When I called back in a few minutes I got a different agent and it was all the same as I was told, I then went ahead with the upgrade. No cancellation fee was added to my upgraded reservation, and it was the same reservation number, so it wasn't like it was cancelled.
Now I may be going back to Chicago to help family after a surgery.... and I may be making another reservation soon. And now I'm learning that if I make a Saver fare reservation it will cost me a cancellation fee if I choose to upgrade it to a roomette. Maybe I was just lucky, twice? I will be more aware now.
There is tremendous variation between the actual policies and what the agents do. Many are very helpful and knowledgeable, and many have no idea whatsoever what the rules are, what the trains offer, etc. So you probably got lucky. That said, if you're sure that you want to end up with a roomette, just start with a roomette. If you'll be fine with coach, get a saver fare.