There is almost unlimited number of ways to hinder colony spam. Endless Space did it somewhat right. GC2 did it fine with economics limitations. Limiting range, more serious penalties for extra colonies, galaxy being a dangerous place in general, maintenance of colonies depending from their range from nearest planets (same for Starbases, btw, so no more spam), more planets types.... A lot of choices.

But i get a feeling that "superior" GC3 AI could handle nothing of it. So his strategy is colony spam only.

On huge map with gifted AI it has no problems with approval with around 80 planets each.

Well since I wanted to post something helpful.

All colonies should have TWO different kinds of population: residents and colonists.

Colonists "grow" from population, and when you take them into your colony ship, they are gone and you can't take more people.

Or call them "adventurers" and they can be soldiers too... Just don't make them unlimited.

Quite so.  What annoys me is that GC2 released in much the same state but over the years the bonkers stuff was steadily evened out.  Why those same lessons need to be learned again with GC3 I'll probably never know.

For me far too many of the fundamental ingredients of GC3 are ruining the pudding.  IMO the prevalence of linear additive stacking of bonuses stand out as being the root of many of this game's woes: turn 1 sensor exploits that obsolete other parts of the game; mid to late game moves stacking that makes a mockery of having a turn bases moves system, and practically results in you being able to teleport doom fleets around the map at will; tech trees that are exhausted before you've even reached 1/4 of the way into the so-called 'turn limit'; planetay adjacency maths that all but force you to hyper-specialise, etc.  The cherry on this particular unpleasant tasting pudding is that the AI doesn't know how to exploit any of that.  (Not that the game would be any better to play if it did.) 

I take no pleasure from putting such a downer on GC3.  I wanted GC3 to be an improvement on GC2, and in many ways it is but the core mechanics of what makes a good 4X, in all phases of play, are, IMO, far weaker in GC3 than they are in GC2.  (At the moment I can't help but feel the same way I did after having given CivV a jolly good seeing to; a nice looking and performing product but just mechanically not as good as the previous version.)  I'm not giving up on GC3 because SD have a rep for fixing stuff like this over time; I'm just a bit miffed that I'm probably going to have to wait another year before GC3 earns pride of place in my 4X collection.

i don't see a significant improvement in your system - the current LEP/approval system isn't much different (except for the adjustment by map size, which should have been included in the LEP system from the start, anyway), so you'd introduce a new stat that is going to make the game systems harder to understand (both for new players and the AI) when there really is no gain from doing so.

i've played lots of 4X games, many of which had some system to nerf REX (rapid early expansion) aka ICS (infinite city sprawl) strategies. the best anti-sprawl system i've seen so far was Civ 4 - they simply used money as the limiting factor. that's easy to understand and reasonably realistic. new cities are a drain for your civs economy until they develop enough to pay for their own upkeep. and the upkeep per city grows as the civ grows, representing the increasing cost of logistics and administration. at some point (based on map size) you'd reach an upper limit of city maintenance, so new cities would still start "in debt" until they were somehwat developed, but the system can't spiral out of control.

if you could pay for 30 cities, you could pay for all the cities on the planet. to get to that point, you'd need a strong economy and/or somewhat advanced tech. good commerce cities develop slowly, but once they are up and running, they can pay for lots of things. tech unlocks better governments that allow you to make more money (or spend less), more trade routes that pay for (some of) the per city upkeep etc. 

i think that last paragraph is also very important for an "epic game" feel. at some point later in the game the initial limitations should be manageable. it's a good idea to throttle the initial REX, because it's a stupid strategy. it's uncool if that same mechanic scales infinitely and still holds me back in the "exterminate" phase of the 4x game. 

translated into GC3, i imagine we could start with a relatively high colony maintenance (just put the maintenance on the "colony capital" building) that increases for every colony, much like LEP increments the approval penalty for every planet. you can pay for expansion with a strong economy and unlock techs that gradually reduce the colony cost (the government techs are already in the game, just change their effect). this will slow initial expansion down until your economy worlds are online and it will still be a drain until mid/late game. at some point you'll be an established interstellar empire with a solid income and some advanced administration techs, so you don't have to worry about the negative effects of additional planets any more and can happily colonize some leftover planets in a remote area, or conquer a rival or two.

In theory. In harsh reality, against gifted AI, after initial rush, while some of your new colonies grow up a bit to the point they can spam colonies themselves, you can start spamming military ships (you don't need them even to be effective) and AI get easily scared by your power rating.  So they'll hate you due to "war frenzy" or something, but don't dare to attack even if you ship are somewhere else. And later due to your extremely talented colony management(in compassion to AI) you'll become much more powerful than AI. Later AI even help you out by colonizing extreme planets inside your ZoI and presenting them to you via cultural flip. 

I disagree. This is exactly the right way to do it. When it's done right that is...

It shouldn't be inherently easier to make a "taller" or "wider" empires. It's supposed to be a strategic choice. And the main point of "punishing for size" is making the management of the size a gameplay element.

Might as well emulate ship rebelions, separatist factions, elections, royal inheritance, civil wars and ruler marriage. Yeah right...

NOT happening. And that's a good thing.

If imperium of men doesn't exist neither should this. And it doesn't.

Besides the obviously missed fact that size management is a highly valued gameplay factor, empires of infinite sizes are simply unreasonable. The whole game is built around power struggle (so we can't rule out this factor from the civilizations in question), and power struggle is what makes empires fall apart.

That said, maintenance is a poor detrimental factor. I'd prefer a TM penalty.  Possibly along with penalties to other things like influence or population growth or even combat efficiency. C5 had a perfectly working system for that... although they changed it so many times I can't say which exact version was perfectly working by now... Well, at least the concept was more or less the same all the time.

As for expansion vulnerability look at how ES did it. In there everyone starts in "cold war" state, which basically means you can attack anyone and anything as long as it's not within anyone else's borders. And borders didn't appear around a colony for about 30 turns after being founded. Not to mention the ability to kill the colony ships and scouts.

The difference from what we see here was in the fact that while such "hostilities" weren't exactly strengthening neighbourhood ties, they didn't require you to outright declare war on all those pesky neighbours.

Sigh... this is what I miss from ES the most... back in there you didn't stake territory with colony ships, you took it with war fleets and held it with war fleets.

And in here you can't even be sure about the land within your own borders. Honestly, we should be able to kill at least the vermin that have crept into our own territory.

It may look far from the topic, but it isn't. The amount of land you can "stake" is a huge factor, and with stronger AIs behaving as they do now you simply can't allow yourself NOT to grab as many colonies as you can reach.