I'm really getting upset realizing that more and more Amtrak conductors are being negligent to their responsibilities by not offering onboard upgrades.
Something to consider when booking a sleeper on the same route is the fact that you could be looking at paying a good chunck of the rail fare over again, though probably still chapter than a room the whole way. IE: LAX - SEA may be $106, but LAX to San Jose may be $54 + San Jose to SEA another $103. Sleepers also tend to price out higher initially with additional distance not adding a whole lot - especially if you are trying to avoid a sleeper during the day.
So I just ran some real numbers, and I figure you can save $9 by booking separate legs. (get roomette in SJC) You can't book a multi city because the connection times are too close (! Same train?!) So you'll need two itineraries.
For $9, get the room in LA, and that'll pay for your lunch. To save some real coin, you'll have to switch in Sacramento at midnight. (around $55)