I too have some comments on the behaviour of the AIs in the campaign. My first notice was that even on masochistic settings they expand very slowly. OK, in one mission it was the bug that dumbed them down, but I invested too much of my time to restart that mission. In most other missions I've been constantly out-colonizing them with such an ease it was not fun anymore. I see two reasons for their slow colonizing, one is related to bad AI decision, and the other is related to bad starting conditions.
1. In all missions I started at war with one or more AIs. I don't now exactly what they did in first few turns, but two graphs tell me what likely happened: their military strenght graph went almost verticaly up, and the treasury graph went almost verticaly down. Obviously they were buying warships while I was buying factories and colonizers. And they didn't stop at twice my mil strenght, they were buying warships until they ran out of money (I amost heard their panicked voices crying "My good, we're at war and don't have ANY serious defense! AAAAAaaaaaa!!!
"). After that they had lots of maintenance expenses for those ships, that put them even deeper in the hole. So until they get out of that hole they weren't able to produce much in terms of development. But for getting out of hole so early they needed population to tax it. And so we're at the second point:
2. In campaign we start with 1B population on our starting planets, not like in sandbox mode with 8B. That 1B pop produces about three times LESS money than 8B, and it takes about 30 turns of ideal 8% growth (3% base * 100% bonus for approval * 40% race bonus - well, not sure if those numbers still hold in DA) just to get to 8B. So a carefull pop management is MUCH more important. But the AI was in serious financial hole and could not afford that, so it taxed them high, and the circle was closed.
What I'd suggest to change in AI behaviour is it should check the threat level from an opponent it's at war with. The threat level from my civ was low: I had only two starting armed small hulls with a single laser, was really far away from them, and my propulsion tech was only a basic one. So they should've built some defensive ships just to shut up those panicked voices, and kept growing their early economy, because that's the needed foundation for almost everything else in the game. At least that's what I did.