I agree with some of your observations, but disagree with others.
First, the engine re-balancing really does seem to hurt the AI. Put the 8 points into getting plus 2 speed and then search up to warp drive and you are just about unstoppable. You will get all the anomalies, and your basic move 7-8 ships can out react the AIs move 1-2 ships. Add in Super Warrior and you can field some pretty fast first strike cargo hull fleets, use your speed to move in and kill, then retreat out of the AI's movement range so they never attack you.
Second, I disagree with you on the espionage... it is plenty powerful, maybe too powerful. I can't ever kick out a spy every five turns later on... I'm limited to spending 25% of my income towards spies. After the first fifty or so it starts to take several months for the next one no matter what I do. The trick to getting them to work is concentration, only hit one enemy at a time.
Because purchasing spies is on a curve, the more enemies you try to spy on the more you are at a disadvantage. Say you kick out 20 spies in a year, and each of your enemies kicks out only 6. If you concentrate all of your spying on one person, they can only neutralize a few of your spies, and you can completely shut down either their industry or research... sometimes both (numbers are there for illustration, you can't actually shut down anyone on a larger map with a meager 14 spies). But if you try and spy on three enemies, you will barely make any progress, even though they are not committing much of their economy to espionage. 18 of your spies will get killed by 6 cheaper spies from each opponent. However, successful espionage is so useful it almost feels broken, but the key is to take your enemies down one at a time.
Asteroid fields can become a big deal if you use a lot of spying, because it represents industrial points you can't shut down. However, I agree it is not worth using your own resources to create mining. The AI rarely hits you with enough spies that you need a secondary production source, and mines are easy to culture flip. Influence starbases build faster than upgraded asteroid mines, so steal your opponents work after they took the credits to create the "asteroid farms" for you.
I agree, the new colonization depth is excellent.
I also agree that trade routes seem to do less. I know in the previews for the game they said that now trade routes increase in value over time... but my last DL game I was able to get 600 per turn from trade, I've only once broken 200 per turn in DA. Either way, trade doesn't make enough of a difference for income, but because it effects what AIs think of you it is still a useful tool. Also, they further reduced the number of trade routes, making it even less effective. Trade tech used to give you +3 routes, now it only gives you +2

I must say I LOVE LOVE LOVE how the new combat system effects mixed fleets with one (huge) capital ship with supporting small and medium fighters. As long as you make your big guy mean enough that the enemy targets it, you can really smash through overwhelming odds. This is because even old, low tech fighters are now useful in groups, given that each shot reduces the enemy defense for the round. Those swarms of support fighters can now kick out some serious damage, so your high def/weap cap ship doesn't need to survive for many turns. And there is something just cool about watching this sort of fleet fight in the combat viewer.