I agree that there should be more enthousiasm on this movie's board, alas I have noticed that there are very few boards about french movies here. I guess there are not enough french people around on IMDB.
Well so here my contribution:
I don't know if Le Pere Noel is the most popular french movie, but it certainly is in the top 10, along with Les Bronzes, Le coup du Parapluie or Le grand Blond avec une Chaussure Noire. I don't know anyone my age (I am around 30) who doesn't know all those movies. So I definitely they are part of the french popular movie culture.
I haven't seen the stage version (well I have seen it once on TV, but that does not really count), so I cannot really answer that question. I guess though that the actors preferred the stage version, as they were free to make the play "live" and grow better, whereas the movie version has fixed everything.
I gave it a 10, because even after having seen it about 20 times, I still find it funny.
I try to send comments or to answer on boards about french movies, but you are right, french cinema ( and overall european cinema) is underrated.
I see you like Pierre Richard too :) I'm very fond of the ones you mentioned, and I'll add "Je suis timide mais je me soigne", with Pierre Richard and Aldo Maccione as one of my favorites.
I didn't see le père Noêl on stage neither, only the recorded version for TV.
At least, we have a topic for this movie !