I was wondering if anyone has any ideas to share on how to enhance or add a little something extra to box cake mix for flavor?

You can look in the recipes tab at the top and choose the category of cake mix cakes. There are a lot of recipes there. The cake mix extender and enhanced cake mix are used a lot.

There are enhanced cake recipes in the recipe section. for flavor, I would say anything your heart can think of...coffee, peanut butter, mint, carmel, etc. Instead of adding water you can add any kind of liquid--soda, coffee, juice, etc.
There's a book called the cake doctor. I highly recommend that for what you are asking. Check your local library.

I use butter instead of oil and I add in 1 tbsp of vanilla and 4 tbsp. cultured powdered buttermilk. I do mostly cupcakes.

I agree with praetorian2000 regarding the Cake Mix Doctor ( author is Anne Byrn). I use this for almost all of my cakes & everyone always thinks they're very yummy!