This is right up my alley. I play on abundant stars and planets. I then change hab planets to uncommon and extrem hab to rare. However, I have found that setting tends to give me ever so slightly too many hab planets.
So I went into the <mapprefs> and changed the values. Under the 'RARE' setting which controls all things there I simply lowered my extreme planets from .05 to .03.
Under the 'UNCOMMON" heading I went to habitable planets and lowered it from .35 to .27. This still did not seem to be enough for me. I may lower it even further.
I want LOTS of STARS and LOTS of Planets but only a small percentage should support life. I play on insane maps. I found that after dozens of games I end up with about 40 to 90 planets. What this makes the game (for me) is it makes competing for planets more fun and I get that 'WoW feeling when I find one.
In closing I would say just go into your game files and find the map prefs and change the values there. Ideally you copy said file and paste into the mods section of the game and make your changes there. I have found this does not always work. If i screw up and ruing the doc, I just delete and re-verify to download a new one.