K Reductions would be welcome, but one thing I'd really like to see is range increases (to counter the lack of mobility). Especially on the Basic and Flak turrets. I don't think flak needs an explanation. Basic, however, is the "counter" to missile frigates, and they have the same range (less vs mark III or higher frigates), so it's often full fleet of frigates vs 1 turret.
Other random thoughts:
Give Mark III turrets radar dampening immunity?
Grav turrets could probably use a K cost increase, especially Mk.I. It gives a ton of utility for 500.
General turret K costs: 1500 for MK. II? 2500 for MK. III?
I'm skeptical about bigger waves because I don't think they work that well (On a multiplayer 10/10 you can be fighting 30k waves quite regularly and IMO when the wave is just 'more carriers!!' it's kind of annoying although I have no good non-CPU destroying alternative) and I'm skeptical about just using Hunter Killers / world's largest force of Raids because that's just a screw you to a legitimate strategy.
Hmm, maybe after a certain point the AI should get a higher ratio of Starships.
I also love crushing enemy fortifications and such, I don't personally see it as a grind.
I was messing around with various options the other day, and discovered that Beachheads with Cross Planet Waves causes them to spawn on AI planets. They aren't the strongest things in the world, but they have decent damage and range similar to missile turrets. It might be worth a try if you can put up with Cross Planet Waves (I recommend using no-wave warnings with CP waves). Unfortunately, It won't work with turtling AI types, but hey, It's something.
I also second the idea of a more official "ai base builders" option. I like killing bases
.