In regards to the nutritional benefits of heirloom corn you may find this interesting
http://www.sciencedaily.com/releases/2007/07/070730092559.htm
Several of the dark colored corn varieties have 16%-20% more protein than the standard white and yellow varieties everyone is used to. That article is about hopi blue corn, but i've read the same thing about bloody butcher, black aztec, black mexican, and Green Oxacana corn.
I've grown all the above corn except green oxacana and made cornmeal out of them. The only downsize is that they are all but uneatable fresh. The sugars in the kernels convert to starch very quickly so there is an ultra small window in which you can eat them fresh. The second any color starts appearing in the kernels they are tough and chewy.