The unique thing i miss in sins' diplomacy, is, when i have a peace treat with AI, that i can't ask for help or ask for attack a planet, etc.
You can do that.
Just click on any allied planet or ship, and you'll see three new buttons appear on the bottom right.
They'll let you ask for help attacking or defending, and a button to cancel your last request.
In my experience, unlike in most games, your ally WILL listen, too. (Although they often show up to a party a bit late, if timing is important.)
I'd like to see some new diplomacy stuff, too, though.
I looked back at Master of Orion II, recently, and Sins isn't actually missing that many options, compared to MOOII. Really, if you could request from the AI everything that they can request of you, and demand and give planets away, that pretty much covers the bases.
Sins could have taken the exact same game, made the asteriods planets, made the planets stars, kept the phase lanes, and then made the star to star travel intergalactic travel, and added some very basic orbital animations (and varying resources per planet) and made an extrordinarily epic game in scale and delivery. That's all it would have taken. When you zoom away from the stars they turn into galaxies anyway, so I'm not sure why they went with "asteriods" instead of planets. Then have 3-15 planets per star (now planets) with varying levels of resource generation and then you could build defensive structures on each planet and had the epic bombardment weapon as a solar system emplacement. That's my .02.
I'm sorry, but that sounds pretty arbitrary.
There's no real reason that science fiction needs to be intergalactic in scale, instead of interplanetary.
Although I agree that the premade maps with scores of planets orbiting a single star are just silly, I actually appreciate the present scale, and find it cooler than flying between galaxies, which would be a bit much.
As for the "asteroids" surrounding planets, those are called MOONS.
Everyone keeps asking why there are no moons in the game, and then wondering why there are those rocks orbiting planets.

Earth is the only non-gas giant planet to have a spherical moon, so it's not abnormal at all to have irregular chunks of rock around your planet.
There! My post is almost like a mini-bonus pack. I added allied requests and moons!