You've hit the nail on the head for the best ways to use culture - combat bonuses and depriving enemies of colonization.  It should be noted, however, that your culture can be negated if enemy capital ships occupy a gravity well for long enough, and eventually they will be able to colonize it.  This can also make it very difficult to use offensive culture if an enemy fleet is defending your target system.

That said, culture/novalith isn't as smooth a combo.  The AI will often lay low and raise its defenses in the late game, avoiding a direct confrontation with your fleet.  This leads to long protracted sieges that favour superweapons, but assures their ultimate defeat.  Against a smarter opponent, they'll prefer to force a battle to try and change the direction of the game, so it typically doesn't last long enough for culture to build up to "game-winning" levels, and superweapons also force them out of hiding, making a cultural offensive less necessary.

As long as you play Advent aganst the AI theres an evil little trick you can pull.  Just get a forward-ish planet (this is late game by necessity) and build 6-7 culture centers depending on how many the planet supports.  Build them in a circle and drop a starbase in the middle, surround them with beam turrets (with synergy), 2 hangar defenses, 2 repair bays and youre golden.  Nothing short of a full fleet can kill this thing and with culture upgrades it pumps out a good 39-42 culture per second.  Nothing can stand up to that, I killed off an Unfair AI earlier with this.