Yea, I am getting to like 'uncommon habitable and tight clusters' WAY more than even spread of stars and lots of habitable ones. Its just my personal preference. 

I really like an 'island Empire' with med to large voids between the next island of stars. This allows me (and the AI) to build infrastructure inside the Empire up before going out and conqueroring/Culturizing the next area. 

Has anyone used Culture Star Bases yet to flip enemy planets?

I've tried! Those pesky Altarians love to colonize planets in my ZoC and aside from going to war and forcibly retaking those planets, I tried to plop 2 culture starbases next to the planet with about 3 or 4 upgrade modules each and still their planet was pushing back my influence with ease (and apparently without making any influence generating structures since their planet stats bar for influence growth showed 1.5 after 50 turns!)