I agree however Zidane alone isn't enough. He has to be backed up by an efficient defensive midfielder who can give him balls. That was the case with Deschamps at the Juventus, or with Makelele at the Real.
Zidane's return isn't the only one which is important. And I'm pretty sure that he wouldn't have joined back the team without Makelele to back him up. Thuram's return is also very important as a central defencer such as him considerably solidifies the whole defence.
Anyway, all this to say that before the return of those 3 guys, it's clear that France played very poorly... mostly because most players are totally unexperienced. It's clear the team is better but as I see it, it's essentially a transitory team. Zidane, Thuram and Makelele's returns are important because they may succeed to qualify the French team for the World Cup (which isn't done yet). This can give experience to the rest of the team once they'll be definitly retired.
Playing a world cup is very important for players selected in their national team. Maybe that with the experience they could get in Germany (if they're qualified, which is far to be done), the younsters of the French team will be able to become performant for the euro 2008 or the WC 2010.