Delete the quotes and enter a number or variable and it works as you'd expect.
"X is " + str(Sprite.X) + " and Y is " + str(SpriteY) + ", and the variable is " + str(Sprite.Value('Variable'))
You can use the & operator to concatenate any variables as text. For example, you could create the same string with:
"X is " & Sprite.X & " and Y is " &Sprite.Y & ", and the variable is " & Sprite.Value('Variable')
Looks a little cleaner and is easier to edit that way.