The easiest way to get less noise is to generate a larger image and down scale it with an image processing application. Under Mac OS X, you can use Preview application and its Tools > Adjust size menu item.
In the next version, there will be also the ability to request better quality setting for SunFlow, at least by changing some program parameters (it's already programed with -Dproperty=value Java parameters but not sure I will show these advanced parameters with a nicer user interface immediately).