Every Nintendo board I've been a member of invariably has a sprawling thread with people listing their friend codes and whatnot whether stickied or otherwise; sometimes two, with one being a list of individual games.
Given that we have such a friendly and active community here why not have fields for friend codes in the profile and some kid of database search function where you can look for friend codes by user or by game title? Couple this with an messaging function (especially cool if you could register your Wii itself to receive messages from NL) and people could then add codes and notify people they've added their code.
I think this would be a great benefit; I'm unaware of any other matchmaking service like this. It would be most awesome for games that lack dynamic match-making capability like Monster Lab or ones that don't have an active online community like Alien Crush Returns or Cue Sports.