In August of 2010 we were returning from Florida on the Silver Star and we had the last bedroom - I had booked it through AGR about 4 hours prior to the train departing Orlando. The next morning we met a young mom with two small kids in the diner (for breakfast) and she mentioned that she had upgraded at Savannah GA to a Roomette. She was quite happy with the upgrade, it really changed her view regarding traveling by train. I think she paid $75 or so, can't recall, but it made a big difference.
Then on my next trip - that December, we had a roomette on the Cardinal. and the Amtrak crew was promoting available sleeper rooms on the PA system. They even brought folks up to our Viewliner car to look around and see the accommodations. So in that case, the conductor was actively trying to sell sleeper space. And on the same trip - later that week, we took the EB east from Portland to Chicago - and we had a Bedroom to Wolf Point, and then a roomette after that. When I asked the car attendant about keeping our bedroom to Chicago - he retrieved the Conductor, who offered us the opportunity to upgrade to bedroom (after Wolf Point), but the fee was rather high, since we were traveling on a free ticket (AGR award).