I think using GUI, mouse, and keyboard effectively is important to make a game fun. While it is true that Roguelikes typically rely solely on the keyboard to be interfaced with, I do not believe that using a GUI or mouse to be mutually exclusive. For example, the mouse would be good for looking at objects on the screen and for tool-tips, while a keyboard is good for accessing many screens quickly, but the GUI is very useful for stuff you want people to easily pay attention to, which is very useful for new players and keeping the player informed.
As a gamer, I feel that having Roguelikes to only use the keyboard and ASCII is anachronistic. One of my favorite roguelikes, Castle of the Winds employed graphics, and had a GUI that was very accessible. For example, there was a quickbar for spellcasting, a paperdoll inventory which made it easier to manage items, wand belts, backpacks, and the ability to quickly examine items by mousing over them and right-clicking for details. In short, by making it easier for the player to understand and interact with the game, the player had more options in how to play the game.
Contrast this with the new military menus for Dwarf Fortress: Most people don't understand them, so they don't use them. This is bad, because the military is an important feature, but since people don't like messing with that menu, it by default becomes a liability and chore. As such, I feel that sticking to tradition for Roguelike interface principals is a bad idea. I think most people play roguelikes for the gameplay, not the ASCII and keyboard aspects. So it shouldn't hurt to rework how the player interacts with the game, if the goal is make the game easier to play with.