I actually tried to create 10 planets per star, but it was a mess (3 planets overlapping, etc). As I was doing this, I found out that the problem was that even on high density it was set to average about 3 planets per star. So it was a very quick and easy fix to change it to favor 5 planets per star, and that makes a big difference in the game play.
Note: With 5 planets you don't get a lot of asteroids or gas giants, so I think that Normal density will give better variety.