(which I'm going to tentatively define as governments where a noticeable proportion of elections have surprising enough results to be worth betting on)
Is this really key feature? Lots of elections considered perfectly democratic are more or less predictable. I mean you do have places like Norway or Japan where the same party kept winning for decades in a row. Once you knew who the party leader was before the election you would also usually know who the PM will be. Who will ascend in the Chinese Communist Party next is if anything less predictable than if say Obama will be re-elected. Also the conclaves often produce surprising choices for the Pope and they are elections, but I don't think most people consider the Vatican to be a democracy.
Fair enough. It was a tentative definition.
Another angle is PJ O'Rourkes idea that societies which are good to live in have rule of law. Unfortunately, I don't have convenient access to his description (if he's got one) of rule of law. It would be in Eat the Rich.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.