multiple media centers/Trade Ports/Refineries on a planet?

Trade ports and cultural centers stack at a nice even rate regardless of how many you build. If you build a culture center and it gives you 2.5 points of culture spread, three will give you 7.5 and so on.

Resource extractors, on the other hand, will only be affected by a certain amount of refineries (usually 3) in the same or neighboring gravity wells so they will only help up to a point. You can check how many refineries you'll need to max the effect by looking at the 'Quota' statistic in the info-tab on an extractor.

It's worth noting that sometimes you WANT to stack as well. Searching planets sometimes comes up with resources that add bonuses to trading, for example, so why not build a couple trading stations if the site is safely behind your lines.

-- Retro

Refineries have maximum benefit. Also, culture from culture buildings varies GREATLY from planet to planet. Your homeworld will usually make 5 culture per building, while some desert only 2.5.

All culture facilities generate the same amount of culture. This culture is divided among all the phase lanes connected to the planet. A single planet with many phase lanes will pump out far less culture along each line.

The culture number that you see is after the culture is divided.

Thnx, this actually makes more sense hehehe. Since your homeworld usually only has 2 lanes to it

Aye, refineries max at 3 per extractor(this includes all extractors both in the gravity well with the refinery and all extractors in gravity wells directly attached to the gravity well with the refinery) for inhabitable systems, and 4 per extractor for uninhabitable areas. The exception is the Advent. They can 'convert' a trade center to a percentage boost to extractors, in the same gravity well only. But this doesn't seem to have a limit. A great tactic might be to convert four trade centers on an ice planet to double its resource output!