One such suggested correlation was the rise of the state and a sense of community, which I (from my armchair) would dismiss as you're probably less psychologically bound to your state than your immediate community. Another suggestion is the rise of propriety and good manners, but I feel that suggestion is an effect, just as the murder rate dropping is an effect. From microeconomics, I would suggest that our valuations of other people changed for the better. This could be caused by either increased trade (killing off possible trade partners is bad business, and trade in a time of haphazardly enforced laws requires trust), increased education (higher personal self-value means less willingness to risk losing one's life, this would also cause people to adopt methods of advertising intelligence, i.e. eloquent speech, good manners, etc.), and of course there are other causes that might be found.
Re: the Fat Kreme Combo, try it without mustard first. I think it's much better that way.
People cheat all the time. Whenever possible, we use shortcuts to get as fast as possible to our goals. Watching Harold Bloom on BookTV, I see an intelligent old man who uses acting to drape himself in the cloak of wisdom. It's not that he's dumb, rather it seems that he at some point learned that acting intelligent platforms your already intelligent ideas. But, as one ages, these worn phrases and mannerisms start to ring hollow.
Harold Bloom, though, did remind me that I've been neglecting poetry. He mentioned Dickinson and Anthony Burgess' Nothing Like the Sun (fun unauthorized biography of Shakespeare's life ;). I think my next book club suggestion will be a collection of Dickinson poems, but if everyone balks on poems, Blood Meridian.
My mistress' eyes are nothing like the sun;
Coral is far more red than her lips' red;
If snow be white, why then her breasts are dun;
If hairs be wires, black wires grow on her head.