I guess you just lose the ability to distinguish between areas past some density, right? What would be a good way to improve it… maybe apply some filter, Lanzcos or whatever?
The technical term is "viewshed analysis", what areas are visible from a given set of points. Any competent GIS system will have ways to do it, but peakfinder.com works pretty well as a more visually interesting demo.
Guess I didn't read the parent closely enough. Thought it was asking what the best way to figure out the actual coverage without arbitrarily increasing line width as you zoom out.