I run tours on the Gulflander, Savannahlander, and Spirit of the Outback in Qld. They are terrific trips.
Ken on the Gulflander, and Leigh and Wil on the Savannahlander are great guys, and make the trip fun.
Chicago to LA would be the Southwest Chief on the old Santa Fe mainline, which route 66 parallels for much of its journey. Unfortunately the climb over Raton pass, and descent of Cajon pass - both famous Santa Fe scenic grades - are in the dark. The Red Cliffs, which were an icon of the Chief, Super Chief, California Limited, El Capitan expresses, should appear around breakfast time, but Amtrak trains are notoriously late.
I also wouldn't mind Chicago-Seattle over the old Great Northern, on the Empire Builder; or the California Zephyr on the Union Pacific to San Fransisco.
Empire builder is the furthest north, and runs through the big Cascade tunnel.
California Zephyr runs through classic mesa country, Cowboy towns like Cheyenne, Laramie, Green River, Medicine Bow; and over the infamous Donner Pass.
They'd all be wonderful trips. Sleeper is the best way to travel. Coach is very cheap; but lacks your own facilities, access to the diner, or a bed.