Culture is a secondary mechanic. You can't really win games through culture directly, but it can help in various ways:

- Culture increases allegiance of friendly planets. You'll notice that each jump away from your capital reduces the planets' allegiances. One jump away and the planet is already at 90%, only generating 90% income from the taxes and mines. Culture raises the max allegiance by 10% on every planet affected by it, so across the empire you get higher incomes. The Advent have a tech that further increases max allegiance (another 10%) through culture.

- It decreases hostile planets' allegiance. If your culture overtakes an enemy's and fully spreads to a planet of theirs, that planet will start losing allegiance. When it drops to 0, the colony will rebel and flip to neutral. The process is somewhat slow, but still there. In addition, that planet will make less and less money while the allegiance keeps dropping. To see allegiance gain/loss/status, select the planet you want to look at, and at the bottom center of the screen to the left of the portait there will be some numbers. The top is the current health, the middle is allegiance - hover over it to open up an info card that has allegiance stats.

- Each race has friendly culture bonuses. These are researched in the culture techs. The TEC's ships recharge antimatter faster in friendly culture. Vasari ships do more damage, and Advent ships have higher shield mitigation so they take less damage.

Yes, culture spread stacks. The way it works is that every jump diminishes culture spread. The more culture you generate, the faster and farther it will move before diminishing completely. In your example, the left over culture from your capital should be added to the output from the new colony, but the info cards will not show this, they only show the raw culture output of the planet (hover over the planet, and it will have a line for culture/sec).

That said, allegiance gain/loss is actually capped. So lots of culture can overwhelm an enemy planet faster, but it will still decrease allegiance at a capped rate.

Not really, unless you don't mind losing culture bonuses and slowly losing planets due to hostile culture influence. Each broadcast centre generates a certain rate of culture. Scuttling all of them drops the rate of culture generation to zero, hence, your culture ceases to exist and hostile culture can take over.

Wait you mean, if I scuffled my broadcast centers and there are no hostile cultures within the closed star system.  My culture would still drop to zero on its own? 

The culture goes away....ever notice that when you blow up an enemy planet with culture stations, you can't colonize initially, but if you wait around a bit, soon you can?

I'm running a Culture Expiriment...   I've started a game wiht the Random Medium size map with 2 Medium opponants.  I'm now in a position where I own 50% of the Star System and I have them outmatched militarily.  I could crush them and finish the game at will however I'm going to see if planets will flip allegiance on culture.

I've built up a number of Broadcast stations or Temples of Communion, whatever, and I'm running a raiding fleet around each AIs territory taking out Trade Ports  and Research facilites (to keep them broke and teched down).  Of course these raids are primarily search and destroy missions for their MediaHubs and TempleOfCommunions. 

Soon my culture will over run theirs...  lets see what happens.

Hey does anyone know if Culture confers a combat advantage?  If not, whats the point of the Culture Cannon?

Thanks
    snazzed

The Deliverance (aka the Culture Cannon you refer to) also gives your ships a temporary 15% damage bonus when they are in the gravity well of the affected planet.

The experiment continues...  no flipping planets yet...  I'll play another 2 hours and keep going until my culture has spread to every planet in the system.  If nothing happens 2 hours after my culture covers 100% of the Star System, I'll call it quits.

Side note:

I've been in here and asked questions about the inner workings of culture and, previously, economy stuff.  Is there anywhere that the inner workings and details of these systems are laid bare?  Rephrase:  Is this stuff documented anywhere?

Thanks
     snazzed

The 10% extra is actually 6% from culture and 4% from research. The first 2% from culture are Tier 2, the next 2% are Tier 4, and the last 2% are Tier 6 (all of which are prerequisite for the Deliverance Engine), all under the Harmony Tree. The remaining 4% comes from a Tier 6 shield research in the Hostility Tree. This means an Advent player must construct 12 labs (6 of each) before being able to gain up to 10% extra mitigation.

There are cases where the Deliverance Signal is unable to overtake enemy culture, so the raiding Advent ships don't get the 6% provided by culture, though they can still get the 4% from research, which is permanent once researched.