(3) ...extreme govs (peace or agressive) have much less chances in practice. :(

(2)
Best stay foccus on materialism or individualism about govs (scientific directory or oligarchic plutocracy, for exemple) and equilibrate with specie traits to have other bonuses too (Like strengh, cleverness or pop growth, etc: those giving bonus in 3 main valors).
In my xps in VH its both better chances to hope to prevail.

Militarism & xenophoby are very intresting about influence (wich is also needed in big quantity) but u pay too much fast ur agressivie doctrine by quick DoW of neighbours and u fail coz in VH u need some 100to120years to reach credible fleets and hope to hold the lines in conflicts.
Its frustrating (i prefer agressive govs) but seems obvious from my xps...

(1) Only efficient govs in VH are those advantaging u highly in very earlier game (like oligarchic plutocracy) or any "neutral" (not agressive/not slaver (sector bug about collectivism): dont have time to grow before being attacked, and not peacefull & fed either: there, u are blocked later by poor diplomacy of AI and unusefull federation in offensive purposes or extention of borders purposes...