What cheats, err "bonuses" do the AIs get at demi-god and Sid levels?
Details will be wrong, but at demi-god, the AI has a 70% cost factor (so everything costs .7 * your_cost -- e.g. a swordsman costs 21 shields instead of 30). At DG, the AI civs also start with an extra worker and a few units (2 offensive, 4 defensive? Something like that) and I think gets a slight bit of free unit upkeep (4 + 1/city or something minor). This level does a nice job of bridging what WAS the biggest jump -- Emperor to Deity -- from pre-C3C.
Sid gives the AI a 40% cost factor (12 shield swordsman, which gets scary fast), plus a ton of bonus units at the game start -- 2 settlers, 3 workers, 6 offensive, 12 defensive, I think. The Sid AI also gets a fairly hefty free unit support. Again, the exact numbers are probably off (I don't have the editor in front of me, where all this is stored/shown), but it's something like 20 free units plus 8 per city, above and beyond govt. support. That's actually not high enough, as a fair number of Sid AIs will choke on their own unit support cost and hurt themselves. The Deity-Sid jump is now the biggest. Why not put in a 50% cost factor AI? <Shrug>
Both levels also encourage AI-AI trading, compared to Regent. At DG, an AI will take like 80% of the cost of something instead of the full 100%, which encourages trading. At Sid, I'm not sure, but there's a LOT of trading, which is both good and bad.
And has the AI improved since PTW?
I think it's gotten worse. The barbarians are really stupid now. The city location algorithm is worse. The AI won't attack armies when it should and doesn't build/fill them intelligently. The PTW AI was pretty good, across the board. The C3C one appears to be a step backwards, which is really unfortunate.
I beat Sid pretty regularly now and deity is even more of a cakewalk than it was in PTW. Unfortunate, really.
Arathorn