I just finished a game on Tough, on a Large galaxy with 9 opponents. I usually play as custom with +20 social/military production and +50 research. I also usually go with Industrialist (+20 social/military production).
This time, I went with +50 diplomacy, +20 research/economics, and Populist (+20 morale/diplomacy). This meant that I started the game with +70 diplomacy...
I won the game EASILY, without ever going to war. With that much extra diplomacy, plus researching diplomacy techs, I was always able to make trades that were ridiculously in my favour, so I was always leading the tech race. When it looked like some of my aggressive neighbours might be getting a bit antsy, I just built a Spin Control Centre and dropped 8 crappy small-hulled ships on the planet. Say it took me maybe 15 turns or so to build 8 small ships... it also brought my military rating from 0 to 270, which scared off everybody. I didn't need to build any more ships until much later in the game, when all I did was build 8 crappy large ships and drop them on the Spin Control Centre, restoring my apparently amazing military dominance.
I won the game through a Diplomatic Victory, allying with ALL 9 of the other races, including the militaristic ones. I never had to go to war with anybody at any point in time. I could have easily won through Conquest as well, since I dominated the tech/economy races.
My real question is does anyone else think that the combination of extremely high diplomacy with the Spin Control Centre seems more than a bit broken? I really had a pathetic military compared to anyone else, but with the Spin Control Centre nobody was even remotely willing to challenge me... It wasn't a satisfying game.