Settings for extreme planets

A rather late reply as I've been on holidays in the past weeks...

Anything that increases the number of planets in your galaxy will also increase your chances of seeing higher quality planets (with the exception of homeworlds and their secondary, those planet qualities are not randomized but depend on the race you've chosen)

E.g. larger galaxies, higher planet density, more habitable planets

  Minor races (up to 8 in DA metaverse games) always get a high quality planet,  but you have to conquer them which can cause "tendancy to conquer others-" in your relations with other races.