Im not sure how to feel on the cant spy on allies thing. On one hand allies do spy on each other, and it offers more than 1 way to slow down someone. OTOH, allying someone to keep them from ever attacking you, then destroying them with your spies isn't hard to do and pretty cheap. Everybody allying each other, or staying allies until the end of the game thwarting the AIs chance at winning is not very logical either, even if its good for roleplay. Late game should be more like a few key players with everyone else who isn't competitive backing another player.(here is where diplomacy can matter) The key players shouldn't like each other.
Perhaps rather than banning it outright, they make doing it a lot riskier. Perhaps Higher catch/fail chance. Maybe something else like if caught, you immediately break/prevent renewal of the alliance and possibly cause a betrayal emergency.
Edit, i not against GC being toned down, but idk if they needed ALL of those changes. 1 or 2 of them would be fine.
I am looking forward to the other changes and the scenario.