See it from another perspective:  American movies may be allowed in many countries, but if the US gov was to start "bombing" tracts telling people of these countries that their governement is bad, their policies are bad, they should overthrow their government and bask in the glory of the USA as a new territory, these governments would not react too well.

So, in my opinion, it may require tweaking, but at the same time, it's kinda expected that the AI will react badly if you try to flip its empire one planet at a time.

I think if anything, the AI does not react quickly enough when you expand your influence making it too easy, especially if you play benevolent with those influence perks.  Converting all planets and starbases to your culture should result in an immediate dow from all AI concerned.

At the same time, I recognize that it's silly that there is no border and the AI can colonize and build starbases everywhere it wants.

Regular people doing stuff like this, this, and even this is one thing... the government explicitly doing it in their metaphorical front yard

   as others have pointed out is one of the fine lines governments shall not cross without consequences.

about b.

If the AI does not react when you build/extend your influence and start flipping its colonies, than it becomes too easy.  Yes, it's one way to win, but the moment your influence becomes really strong, there's no way the AI can compete, even with massive build of cultural centers, there's no turning back.

And for a civiization like the Drengin, wich are better at war than spreading influence positively, if they were to simply stand by and fight back only with cultural buildings, they would lose 100% of the time.

Imho, the AI should react with war if you threaten its culture to the point of making it lose the game.  Influence let you avoid some conquest, but not all of it, and it shouldn't be that way.  As I said, if you play benevolent, it's way to easy to win a cultural war.  The moment you have the perk that lets you flip planets&bases to your side, if timed properly, it simple spells the doom of your ennemies.

You could use influence starbases to boost the influence of your own colonies. I never build influence starbases in my opponents' territory; neutral space and edge of my zone is fair game, but never next to another player's planet. You could also refrain from building influence starbases in their space until you have a non-aggression treaty with them.

The safest way is to build at the edge of your territory, and not let their range cover an opponent's planet. I do this all the time and they ignore it.

Thanks for this, you are right, you can pressure borders this way with little or no diplomatic consequence.

My 2 cents.  I think the game has it pretty close to right.  Influence from a planet is not the same as a SB dishing out influence.  SB's are offensive tools and should be treated as such.  Place a SB near my worlds and if it starts to impact me I'm going to blast it.  That's what we would do as humans.  So why can't the AI react the same way?  You want a passive aggressive approach without any consequences.