Sarko has a history of this, and it has often paid off. Also, it's possible the North Koreans might accept bilateral negotiations with the French as a substitute for bilateral negotiations with the Americans.
The biggest difference is that Sarko is not the one going, but instead the Socialist and former Culture Minister, Jack Lang. It makes a lot of sense for Sarko not to go himself, but I wonder how much the North Koreans will care about a former Culture Minister. We had to send Bill Clinton to get our journalists back, though in this case the French are considering concessions that we weren't.
Good luck Land and Sarko. Anything that can break this impasse right now, no matter how improbable, should probably be commended.