Why are there two different properties for what would intuitively be the same thing (value/text)... i.e., vs. a single get/set text property?
Text is a string. It represents the actual text the user sees on the screen.
Value is an object and can be any value.
The reason they are different is because you can use the Combo as a sort've lookup table. So, for example, you might have a database with a list of customers. Each customer has a unique ID Number and a name. If you displayed customers in a Combo, you would want the user to see the names, but you want to save the ID to your DataBase. So you bind the Combo to the list of customers and set the ValueMember to the ID field and the DisplayMember to the name field.
The combo will now display the DisplayMember (name) field to the user. The Text property of the Combo will return what the user sees - the name. But the Value will return the ID field.
How does these properties relate in terms of UltraTextEditor or any TextEditorControlBase
The Value of the control could be an object and the Text will return the string that is displayed by the control - typically the ToString of the object.