This story is a sequel of Barks' "Lost In the Andes" (OS 223), but you can also find references to "The Second-Richest Duck" (W US 15), "Statuesque Spendthrifts" (WDC 138), "The Golden Helmet" (OS 408), "A Cold Bargain" (W US 17), "Horseradish Treasure" (OS 495), and "The Fabulous Tycoon" (W US 23).
First, here is a panel taken from "The Second-Richest Duck" :
There is another panel from "The Second-Richest
Duck" that has been used : Flintheart's Money Bin.
You can see this panel here.
In this story, a lot of panels from "Lost In the Andes" have been used. First, that one, the arrival to Plain Awful :
Then, the first meeting with a Plainawfultonian :
... and their president's :
I also wanted to include those two drawings :
The first is a drawing by Don Rosa for the French magasine "Picsou Magazine" #15, from 1999, that looks much with the page 17, panel 5 from "Lost In the Andes" too, and the second one is an oil painting by Barks entitled "Return to Plain Awful" too, and from 1989 too (the story "Return to Plain Awful" is from 1989). You can compare it with the panel 1 page 8 from the story... I don't if the story has been inspired by the painting, or if it is the painting that have been inspired by the story, but there must be a link!
There are also panels from "Lost In the Andes" used in ,"The Son of the Sun" (AR 102), and panels from "The Second-Richest Duck" in "The Son of the Sun" (AR 102), "Island At The Edge Of Time" (D 91071) (Flintheart's Money Bin), "The Last Lord Of Eldorado" (D 96066) (Flintheart's Money Bin), and "A Little Something Special" (D 96325) (Flintheart's Money Bin).