I've learned the value of "snippet of wisdom" very early - my diplomat has a mere 25 in the skill but I can't tell you how often it has been my saving grace - free to cast, move it two down and give your opponent the fuel he needs to give you cards to play as well...
I've played snippet just because I knew it would give my opponent the point he would need to play a card that would give ME the points *I* needed
also, as someone else has said, losing and knowing what your opponent will fuel you with becomes invaluable cause then you know to stock up on those cards.
The last thing (and I'm sure you've learned this at your skill level) is the valuable knowledge of knowing when to shut up.
When I first started playing the diplomacy game, I was playing cards every chance I got the points to play them. I don't do that so much anymore. By skill level 10 (I'm a slow learner) I learned the value of starving my opponent when I had the lead and making him listen for a turn or two. Sometimes it's important to ride the wave.
I'm sure diplomacy gets a lot tougher higher up, but still... these are the core concepts and if you've gotten that high, I know you have a grasp of them, you're just a bit frustrated
you'll fly past it in no time, I'm sure!