Interesting idea that. I will certainly consider it.
As for the smoothness, this is limited by the number of verts available (pretty much the same in any prog). The only way to make it smoother is to scale down the entire terrain and use a larger brush (or the auto features like heightmapping and autotexturing if its a huge terrain). You could also make it appear smoother in the game by using normal smoothing & clever lighting but only up to a point.
As for the smoothness, this is limited by the number of verts available (pretty much the same in any prog). The only way to make it smoother is to scale down the entire terrain and use a larger brush (or the auto features like heightmapping and autotexturing if its a huge terrain). You could also make it appear smoother in the game by using normal smoothing & clever lighting but only up to a point.