Well, I think it was the same in GC I. I understand the rationnal since it allow late minor not to be behind in tech race. But making them super spies is very annoying. Maybe they should get all techs that is known by at least 2 (or 3) others races.

But I hope the AI will be able to build wisely (maybe rushbyuing some factories) since the available buildings will surely require lots of week to be build

I agree.
Give them:
- all the techs known by at least 3 race (2 if only two races remain).
- a 60% chance of getting a tech known by 2 race (1 if only two races remain).
- a 30% chance of getting a tech known by 1 race (ignore if only two races remain).
- a 10% chance of getting one tech more in each branch (once for each branch).
To give techs, work the tree upward and stop a soon as a tech fails in a branch.

This way:
- a new minor is at least on par with the middle races of the galaxy
- he is likely somewhat behind the second race (depending on how the techs are spread between races)
- he has a chance of getting free stuff that nobody other has (giving you a chance to trade with him and not making him worthless except as a spy )
- he won't have all the techs that only two races share (or known to only one) (the 60% ensure that he'll miss some of them)
- he won't be able to work up very high in a tech branch known to only one or two races (the 60% ensure that he'll fail at some time working up in the branch)

Then, run an analysis of his tech situation : if he looks a little low, give him more ships/money to defend himself against greedy predators willing to seize a brand new class 15 planet. Hence, you also could end up with minors that come in not with a large tech knowledge, but with a large fleet, and which could pose different threats and problems.

i think u should be able to directly ask minor races to spy on other races. for a price of course

or pay them to make a trade embargo with some anoying AI.