If you want a symbol that shows you just how clever Bart is (and how insane the movie Blazing Saddles is), then look no further than the replica of Rock Ridge.

Bart knows that he'll never defeat Hedley Lamarr's army of mercenaries with force alone. So he gets the people of Rock Ridge together and tells them,

"Now, before the sun comes up, we're going to build on this site an exact replica of the town of Rock Ridge." 

When the townsfolk say they don't have the manpower to make a replica, Bart adds that it's possible if the people of Rock Ridge agree to work with,

"Rail road workers. They've agreed to help us make our dream come true. And all they ask in return is a little plot of land they can call their own to homestead." 

So it looks like the white people and black people are going to have to learn to work together if they want the town built.

It's not that the people of Rock Ridge have suddenly become less racist. They just know that they have a mutual interest in defeating Hedley's army. This is really the same case as what we get with the people of Rock Ridge accepting Bart as their sheriff. It's not really about a moral revelation. It's about knowing what's good for you.

So in a sense, the fake town represents two things: 1) how stupid the bad people in this movie are, and 2) how quickly people will get over their prejudice if it means saving their own skin.