I prefer ASCII graphics with a custom, square tileset. There is no question that ASCII is a turn off to a lot of newcomers. I also think the base game would benefit from having a native graphics option.
However, I will never change from ASCII - it provokes the imagination and is easier to parse at speed. I also think that if people spent a few days adjusting to it, they would agree. Most people lack the patience and for some reason refuse to believe just how awesome it is to play with ASCII. I'm not lying when I say that I, too, thought ASCII was unbearable. Back when I started there weren't many alternatives, so I shouldered through learning this weird freeware that was supposedly the deepest fantasy simulation. Then I learned to appreciate ASCII for what it wasn't, and now I can actually describe things as beautiful - the flowering of fruit trees in the spring, the flow of blood down a stream, the assortment of minerals and ores that thread through a cavern.
One downside to graphics is that every pack is different, and so when a person shares a screenshot from one it isn't very obvious what's going on to someone unfamiliar with that pack. With ASCII, ever person reasonably familiar with reading letters has a chance to put together what they are seeing, despite different tilesets or whatnot. Obviously, a "vanilla" graphics pack would be recognizable to all should it become available.