Interesting thread.
Yes, I agree with ssorenn, Sh@dow, and most others. Communicative players tend to be more successful, in general. Contact every player individually in the first turn, not only your direct neighbours. Try to stay on friendly terms with everyone. Continue to talk after a stab. Propose to share information if you've nothing to offer, make suggestions, discuss the moves of others, ask questions, invite suggestions, be polite, congratulate players with successful moves, etc. Complete uncommunicativeness is an invitation to be attacked by everyone.
And not to be forgotten: reread your messages carefully before you send them.
Nevertheless, I can't fully agree with everything written here.
"Contact everyone every turn" - yes, in the first two or three years. I prefer to be talkative afterwards, but I believe that's a personal choice. I'm not convinced it is really necessary to talk to everyone after the first stage, when the game is more or less settled.
"win/draw/success rating is strongly correlated to number of messages per game" - certainly; however, a statistical correlation is not a guarantee. It is perfectly possible to have a solo-victory in a serious game (winner-takes-all, full press, no NMRs) with perhaps 42 messages, or fewer.
That being said, I strongly want to emphasize that your neighbour's neighbours are more important in the long run than your direct neighbours. Don't neglect them, try to cultivate links as early as possible. It can be proven that the two great powers which need each other most, are ... England and Austria (yes, really: http://diplom.org/Zine/F2007R/Burton/statistician3.htm ; table 4)