I've yet to win a game via conquest so far - every time I go heavy military, I end up winning through influence instead, because from capturing planets with massive amounts of influence I end up going straight past the 76% victory requirement before finishing off the last couple of empires.
I know I could just turn off the influence victory, but I think that this situation is hinting at a gameplay issue: that capturing a planet immediately converts all of that planet's influence to your own. Is that really good for gameplay, or indeed does it even make sense thematically? I mean, you've just conquered a planet by force, destroyed large amounts of the population, infrastructure and maybe even scorched the terrain making it unusable. But all of the influence the planet had generated for its original owner is somehow transferred to you, 100% intact? And so, suddenly, not only does the target empire have massively less influence on the galaxy, but the conquering empire has gained what they lost, zero-sum - a double whammy for the balance of the war.
Would it not be better, in both gameplay and theme, to have a planet's influence reset, or at least heavily deteriorate, upon capture? Influence generation would still exist based on the buildings that survived, etc, but it would have to start from scratch, leaving it vulnerable to enemy influence (an approximation of some lingering rebellious population) and generally being less immediately useful for expanding your borders.
Thoughts?