Two questions:

1. Can you upgrade from one type of sleeper to another?

In other words, if I wanted to try a bigger compartment (say, a bedroom as compared to the roomette) but didn't want to pay the difference (on one test booking I did, it was almost double the price of a roomette for the bedroom and almost four times for the family bedroom), can I book a roomette and then upgrade to a bedroom on board for what would hopefully be less than booking the bedroom directly?

2. If I'm planning to do a trip where I'm going to try to upgrade, is there a way I can check inventory to see what travel days are going to be most likely to have room to upgrade on board? If not online, can Amtrak reservations agents look that up? Reason being this: on my standard trip of SIM-PRB on the CS, I'd like to upgrade to a sleeper a) just to see what they look like and b) to experience the Parlour Car. Since I'm on leisure travel just visiting family, I can play with the dates, so I'd rather book a seat on a train that has more sleeper compartments available so there's less of a chance they'll fill up before I board (I'd book it just a few days in advance, although I'd have to balance out the desire for flexibility for an upgrade with the chance that the coach seat fare will go up with a short-notice booking and the desire to use a discount code).

What would the lowest fare bucket for a roomette on the CS from SIM-PRB be? The lowest I could find is a $68 upgrade (on top of a $35 fare--it's a 5.5 hour trip). If, once I know my dates, I can find something close to that (assuming that is the lowest fare bucket), I'll just skip the upgrade and book it...unfortunately, most of the rest of the year I'm seeing at least $100-150 for an upgrade to a roomette.

All I really want is the Parlour Car--will the conductor "sell" me access to just that for a crisp $50 or something?