First of all, people need to stop splitting hairs over what is or is not "hacking". It's pretty obvious from the OP's own post that they meant for this to apply to all aspects of the process. You are making a ROM hack, thus whatever you do to make it, is a part of the "hacking" process, yes?
That being said, I'm surprised at all this "graphics vs. code" nonsense. The hardest part of making a ROM hack, in my humble opinion, is the designing. When you plan out the hack, you must do far more work than at any other step, and oftentimes redo your work over and over. Scripts are made and work, sprites are drawn and look good, but designs are constantly reworked throughout the process. Not only that, but design requires an understanding of all the other parts of the hack, good writing skills, a sense of storytelling, and so much more. While other aspects of the hack require only one skill, a designer must be a Jack-of-all-trades, an artist and a scholar who not only lays detailed plans, but also spends hours in research to make certain that one's ideas can be implemented within the framework of the game you are hacking. At times, this can mean reworking hours or even weeks of planned content to accommodate that one feature that you can't make work quite how you planned it. Not to mention the people skills you need if you're part of a team.
