Amtrak does give the cost of upgrading, click on 'private rooms' for that.
For instance on 30 September CHI to GPK, click on private rooms in the top right hand result and you get $935 roomette, and $3072 bedroom. On the top left result $1072 and $3072.
The right hand result is train 7, the section that continues to SEA after the train splits in Spokane, the left hand one is train 27, the Portland (OR) section.
The bottom results are if you choose to use the day train, the Borealis, to St Paul Minneappolis and change into the following train 7/27 at St Paul Union with about a 4 hour 30 wait. $200 cheaper in a roomette and $600 cheaper in a bedroom, and you wouldn't be using the bed during the day.
Train 7 is the section which takes the restaurant car on to Seattle, Train 27 has a cafe/dome car. So the train 7 section you have a shorter walk for your meals, if that matters.
With that price difference it would be a no brainer to me.7/27 can't physical!y overtake you, if the Borealis was heavily delayed.
I've only personally done a Roomette on Amtrak, I don't mind going down to the end of the car for the bathroom and, traveling solo, dont need the extra space of a bedroom.
I've not done the EB, but have done several of the other Trans Continental trains and the Coast Starlight.