ASCII keeps things squarely in the symbolic realm, and leaves plenty of room for a clean and functional design that just plain looks good. OTOH, tilesets make an attempt to convey actual representations in tiny squares, and only get halfway there. They lose the clean, unified aesthetic for cramped squares of pixel vomit and badly spaced fonts. I think that the ASCII graphical interface is perfectly fine for anybody with enough sense to use the dwarf wiki--it's the functional interface that is the real culprit in turning people away from the game.
To be fair, this is partway problem of game engine:
1) Ascii has overlaps that Tileset has to ahdere.
Symbol for ramp, for example, doubles are symbol for loaded balista arrowhead. And dont get me started on bag/amulet/pigtail/male symbol ... And workshops, poor workshops... Or letter "O", poor O.
Making sensible graphical set is quite hard if you have to follow theese little nuances, and even then it ends up looking bad.
2) There next to no typography.
All characters layoutted to grid where each character has same width. That means that most of text is going to look awfull and be unreadable unless you use symbols made directly for curses.
Hell, whole game is in same grid, so you can not even make large-ish graphics because it would make text huge. There is no reason why it should be so, actual map display could, and should, be separated from user interface.
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Graphics sets are going to look bad by default untill there is UI revamp.