To somewhat echo Wilf's coments, I'm not sure that it will produce a lot of valuable insight, though I guess part of the process is that you never know what kind of insight you'll find until you go looking.

I think you also need to consider situations where the insurgents didn't win, but the democracy came to an end. In other words, one reason democracies don't lose is because if the weak kneed liberal Democratic politicians start to lose, the military stages a coup. Pakistan comes to mind. There may be some examples in Central and South America.

Also - I meant to mention this a couple of times - it seems to me the French defined victory as maintaining their colonies and the British defined victory as giving their colonies independence. Since what most of the insurgents wanted was independence from the British, it seems to me that democracies have a lot more ability to spin the definition of "victory." For that matter, changing the definition of "democracy" invalidates your thesis:

There is debate about how closely the South Vietnamese government was linked to the United States, which was a strong supporter of South Vietnam. The country is alleged by many historians to have been nothing more than an American-backed puppet government, but many others claim that it was genuine democracy (or, at the least, a patriotic movement with genuine concern for the Vietnamese people). An individual's views on the matter generally correspond closely to their views on the Vietnam War in general - supporters of the war often believe that South Vietnam was a democracy, and thus worthy of defence, while opponents of the war often believe that South Vietnamese democracy was a sham.