Well, butter doesn't have much to offer nutritionally besides fat, and sugar doesn't have anything to offer besides calories from carbs.
For a healthier fat substitute, you could spread your cornbread with mashed avocado or a nut butter (both are high in fat, but offer more nutrients than butter).
For sugar, try agave nectar (the blueberries would taste good with that, and it's liquid rather than granular, so the consistancy blended would probably be better).