indeed you do. and its something that actually happens in some situations, for example to attack or defend culturally near borders. I am not sure, but I think there is a cap to it, so it does not rise indefinately.

tbh I do not put a huge emphasis on culture, unless pressed into it. I try to get the tech along the way and spread a few around my empire, so that every planet gets it at least from its neighbouring planet which is enough to raise the allegiance cap for the extra resources. only if I see an opportunity or a threat do I concentrate them more.

but then I do not consider myself a pro, so consider that.

Thanks very much guys!

Im in the habit of placing 1 broadcast center on all of my planets. Crazy?

It's very crazy. Too many broadcast centers will eventually cause your own population to rebel against you, after having to watch the same washed out reality shows non-stop 24/7. Shows such as "The Slave", where contestants compete to be enslaved by a charming Vasari overlord with "eliminations" being quite literal, and "Who Wants To Be a Ship Captain", where contestants compete for a spot commanding a military vessel, to boost the military's need for fresh rookies to send on suicide missions. That's not even mentioning the rather depressing "Where Are They Now" segments for these shows

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.