BTW X, a few questions related to the things above:
Sure thing!
1) If the AI hits 200 and gets a new ship, does this ship somehow disappear (or the AI can't build any) if the AI goes below 200?
Nope, that's the one thing that is irreversible. But having a new ship type doesn't give it more volume of ships, it just spreads out the ships that it reinforces with into more ship types, if that makes sense. So it doesn't increase the difficulty unless the ship type itself is more difficult.
2) What happens if the AI goes over 200, then below, then over 200 again?
I had to check to see, actually. This is probably the only property that is affected by positive AI progress only, actually. In other words, the game keeps track of the total positive and negative AI Progress modifiers, and the negative are completely ignored for when the AI unlocks new ship types. So even if you have +200 AI Progress and -100 negative AI progess, showing a total of 100 AI progress on your screen, you'll see the AI getting new ship types after that point. Here again it's not so much a question of difficulty usually, unlike the actual numbers of ships built, and the tech level of the ships built, both of which are affected by the total effective AI Progress (100 from my example).
As an added note, part of why the game keeps track of the negative and positive components of the AI progress is for having an internal lower bound without ever wasting datacenters. For example, here are the cap levels:
>= 100, cap 30
>= 150, cap 40
>= 200, cap 50
>= 250, cap 60
>= 300, cap 70
>= 350, cap 80
>= 400, cap 90
>= 450, cap 100
So what that's telling you is that if your internal, non-adjusted AI Progress is 100 or more, you can never reduce the effective AI Progress below 30. But! If you kill so many datacenters that it would draw it below the cap, don't worry about that wasting your efforts. There is never a reason to delay killing a datacenter. It's true that in those circumstances the datacenter killing would have no immediate effect, but the next time your AI Progress would be increased, the prior datacenter reduction will keep it snapped to that cap level (assuming the cap level doesn't bump up to a new height).
3) Same for when it goes over 240 and sends out level II ships. Can this be brought down to I again?
Yes, this can get brought back down to I. Same as with the relative volume of ships in waves and reinforcements. Any existing waves/reinforcements of higher volume/tech level won't be affected, but new ones will be back at the prior level.
4) I'm in a 80 planet game (with 79 unknown planets). There are 18 Data Centers, 5 Libraries and 2 factories. I have searched through 15 of the 79 unknowns and found none. The probability of this, given a random distribution, is lower than 1 in 1.000.000. So I suspect the distribution may not be random. Are the goodies somehow distributed further away from me?
Yes, there is some logic in that for data centers in particular. Data Centers will be at least three hops away from you, and the majority of them are always clustered on the planets nearest to the AI home planets (these are the "core" AI planets). Figure that half or more will be on the core planets, depending on the map, and the rest will be scattered around not just directly near you.
For the advanced factories and research stations, those are also going to be at least three hops away from you in most cases, but they won't ever be on core or home AI planets. Their distribution is otherwise random, though, aside from just not giving them directly to you at the start. If you've got a lot of wormholes on your starting planet(s), that might make more planets closer to you and thus the selection of planets at which the goodies can be found a bit more distant and smaller.
Great questions!