This is great advice that extends well beyond Roguelikes.
I prefer ASCII in Roguelikes. And while yes, I do enjoy old roguelikes that were very plain, I'll also say that creative use of ASCII, and colors, and ASCII "animations" can make a game much more pleasurable (and if done poorly, much less pleasurable).
Saying there's no real "art" in these ASCII graphics is having a rather limiting view of what art is. Making aesthetic games with ASCII definitely involves art.
The tiled/sprite based Rogues - I never liked them. They always restricted my imagination, and had poor graphics.
My favorite ASCII roguelike is probably Brogue (available for Mac OS X, Windows and Linux): https://sites.google.com/site/broguegame/
And when you add new assets, you still add some kind of burden to the design. Roguelikes just hit those design challenges much faster than most, since they have a world model that makes it straightforward to get to the part where you have the assets and now they have to be tied together in some sensible way.
Action games have it relatively easier when it comes time to do this design work: You know that the gameplay is mostly going to be about collisions, timers, and finite state. The bandwidth of what can be visualized gives you some hard limits on your design scope. Role-playing, in contrast, can keep piling on details. There's more of a UI/accessibility concern in good role-playing design, something that can produce interesting scenarios without resting on obscure details that the player has to sit there calculating out.
I think it's one of the reason roguelikes are often so deep gameplay-wise. You want to add a new species of trolls who can fly to your game? Just implement the logic and associate a "T" character or whatever. Want to destroy a wall? Remove the "#". Want to make a lava pit? Display a red "~". You don't have to worry about having to create new models, new textures, new shaders, new sound effects etc...
Meanwhile generating interesting levels and tweaking the Random Number God to make the game interesting and challenging without making it unfairly difficult is pretty tricky.
Good roguelikes have a good mix of human-made "scripted" elements integrated in randomly generated worlds. Too much of the former and the game feels repetitive and predictable. Too much of the latter and the game feels soulless and aimless.