Culture spread is reduced when going through planets. TEC has a tech that allows that reduction to be less. Advent just have lots of culture increases and a superweapon which flings a big blob o' culture at a planet. Vasari have SFA
one culture structure every few systems is fine for the back lines. Your 'front line' generally needs a few culture centres per planet (if you plan for it to be your front line for a long time). Having your capital nearby seems to help with culture spread. Advent superweapon wrecks anyone's culture day but their own.
As Vasari. You get salvage for blowing up orbital structures and cap ships... kill things already. Wipe out nearby systems, EVEN if you can't hold them. Raid, raid, raid. Their culture spread diminishes as it passes planets too.
As TEC, a wall, one or two systems thick at the edge of your empire should push your culture fairly deep into their space if it has enough broadcast centres.
As Advent. I KNOW people say the superweapons are expensive, but if you're fighting a culture war, it takes less resources to win it with deliverance engines AND culture structures than culture structures alone. If you have Deliverence engines, you don't NEED to win the culture war, just ... don't lose it and drop a deliverance hit on any system you want to fight in, colonize, or otherwise win at culture. Have a couple of backups for sustained ops. They are also priceless for giving a new homeworld a big boost in loyalty FASTER than loyalty drops at the old site, meaning you will get back the resources used to move it by having 2 areas of elevated loyalty.