I use diplomacy a lot. My game play is to have fun, build an empire, and win the game, in that order. I play on Normal most of the time. When the game is released and scores get competitive, I may or may not play on higher difficulty. I did a little with GCII, but not much.
Diplomacy and all the resources are a big part of the game for me. I trade with every AI major and minor. I don't put a lot of value on borders since the AI is not going to observe them anyway, so I frequently trade with open borders and I find the AI values them at 500-1000 BC, depending on who,when, and where. I frequently trade for resources. If a minor builds a resource base near me I will either trade for the base or trade for the output. I often trade for over half the planetary resources in the galaxy. I sometimes take 15-20 minutes to play a turn I win some by conquest and a lot by influence, diplomacy, etc.
It is not difficult for me to win the game on normal, but while I am an average, at best, player, I have been playing the GC game for years and I know my way around the game. From reading this forum, I can see that what I get out of the game, is way different from what many others like. Basically, I want a game that does not crash. After that I take what they give me and play it until my interest wanes. It is very likely that I will play this one as long as they are releasing expansions.
At some point I will lose interest like I did with GCII but that's a long way out at this point.