On the topic of ion cannons, currently, every mkIII planet has an ion I cannon(besides the intitial neighbors of course) and every mkIV has an ion II. Have you ever considered making it instead a bin type of assignment? Say for a mkIII planet that it has a 70-80% chance of pulling a ion I, and fill that other 20-30% with other nasty ai specials(alarm posts, black hole gens, perhaps a heavy cannon at every wormhole/guardpost, etc).
Why? As it is currently, most mkIII and IV planets play out about the same once I get a good number of mkIII units, and since I keep the ai progress down where I see mostly mkI and occasionally mkII raids, being able to guarantee myself a ion cannon on capture makes defending these planets perhaps a bit too easy(and somewhat routine). Basically I'd love for there to be a small but significant chance that each mkIII and IV planet wouldn't have an ion cannon, but would have something else nasty to replace it.