Well why not?! If you're going to make brownies from a box mix, vary it up a bit and throw in some healthy fiber for a change! Lynn, from The Actor's Diet, made "idiot-proof" brownies by adding in black bean-puree instead of eggs, water, and oil. She claims in this post here that it was quite the successful experiment!
I know Hungry Girl has a similar trick, but instead of bean-puree, she uses a can of pumpkin for a low-guilt, healthy, but goey batch of brownies. And finally, a friend of mine swears that all a good batch of brownie-mix needs is a bit of alcohol, like Makers scotch. Have you tried any of these ideas before? What do you think?!