We've mentioned three ways of acquiring a new species:
Real conquest of a planet involves expending on armed ships and troop ships, so a lot of PPs that could have been invested on new colonies. This takes a toll on the invader empire (specially if invasion mission fails). I take that as the base case for balance. Also, by lowering stability to zero on invasion, we delay output from the invaded colony and building of more colonies with the new species. Of course, the attacked empire also takes a toll regardless of the result, by losing a colony and/or armed ships.
Exchange by gifting involves no cost currently: each empire loses one colony and gains one colony, with no risk of failure, no need of armed ships or troop ships. This means that early game you are always better off dealing with a neighbour that has a species that complements well with yours: you and your neighbour become the same kind of empire (boring), both can speed up colonization and probably boost research/production with no extra investment or risks. Other players that go the hard route of invasion, or that do not have complementary species nearby (because similar to yours or because no good/adeq. planets for that species in your space), will progress slower. So it becomes a no-brainer to do species exchange early game. That is not good.
For those of us that think that species gifting is OP, for the reasons mentioned above and in the rest of this thread, it shall require some IP investment, I guess comparable to at least the PP cost of the troop ships to invade (something hard to measure, we could use first IP_cost = 10 + 2*population of gifted planet). It's not like we want to make it harder than invasion, just not absurdly cheap.
Exchange by fake conquest involves nearly no cost: each empire loses and gains one colony, no risk of failure, and only needed the cheapest troop ship. And we can't impose an IP cost here since that would also affect real conquest. This is rather bad:
- If game settings allowed gifting (that costs IP to balance it against real conquest), exchange by fake conquest would be an exploit since it could be used to bypass the IP_cost, and hence it would be used, making the IP cost for gifting just a silly rule that forces players to micromanage the fake conquests. I think that needs addressing for the same reasons than exchange by gifting.
- If game settings were "no_diplomacy-no_gifting", exchange by fake conquest is an obvious exploit since it allows to do something supposedly forbidden. So even if you don't buy any other reason, this should be enough to consider fixing fake conquest, regardless of giving gifting an IP cost or not.
In current game, with Magnate PP/RP skyrocketing (and with Omni-scanner researched), Hyperant was given the choice to recover its HW and the bunch of planets I took from him and granted alliance until he decides to break it, in exchange of joining me and o01eg against Magnate. He declined and proceeded to gift all his assets to Magnate, making any resistance from me and o01eg futile. Here there was a story of small allying with big to finish over the losing alliance of smalls.I still dont think this is a real problem though. At least until we define a multiplayer-story which sais that early mixed empires should be expensive to acquire or another that sais all starting positions (and all possible alliances) should be equal. In board games at least uneven starting positions get evened out to a agree by the weaker ones banding together against the stronger ones.
It might be that this is different with FO because you do not have such a good overview (so you are not so sure who is strong) and its hard to strike somebody far away (so you cant really decide whom to fight).
In this game species exchange by gifting made Magnate-Hyperant powerful, but we have more examples on previous games. In one with Alleryn we two got fat thanks to early species exchange (Egassem+Laenfa). TheSilentOne, L29Ah and o01eg allied together and got the win; swaq was first with us, then with them, and (when Alleryn and I were falling down) finally with us again till the end. So in that game we have the opposite story regarding alliances: small ally against big.
Summing up, there is no clear patter for alliance movements, but there is for early species exchange being always a boost (and hence a nobrainer).
So I do think we have a multiplayer-story about mixed-empires should be equally expensive to acquire through the different means (conquest, gifting...), instead of clearly cheaper by one mean that becomes a nobrainer that also makes empires very similar.
For mid game I don't think we need any special mechanic: empires are big enough by that time to be able to engage in invasion missions and have got time to suffer/enjoy their lack/abundance of planets to colonize during early game.
For early game...
Once we get species-integration-into-empire mechanics, we can make integration from conquest harder than from gifting, so that (when allowed) gifting is better than fake conquest, which would address my concerns for games where gifting is allowed. We already have some sort of colony-integration mechanic, stability, that even with (moderate) IP costs makes gifting better than conquest.
But that does not solve the problem when gifting is not allowed, since species acquisition by fake conquest is cheaper than by real conquest.
The only way I can think of is your idea about increasing troops (not for mid game but from start): The fake conquest involves attacking with an armed ship and troops a colony on the turn it gets established. A partial solution would be to set troops meter to target meter when established. Not working for rushers that do the exchange before getting first defense troop tech. So... what about adding a base number of troops from start to every inhabited planet? 6 could be the number (to force using more than one medium-hull troop ship). The first defense troop tech could be nerfed to give another 6 (down from 10).
Natives are not a concern (and do not need being addressed here). We can give them (more) planetary defense and troops to make them not free, at least for CanColonize natives. But the minimum 6 troops patch could work for them too.
The equal-starting-positions is something that would be great to have as an option at game settings (you might want it or not). That's a different subject though.