I don't expect to get much support, but this has been bugging me for a while, and now that another Nationals has begun, I have to get this off my chest:
If "good luck" is not meant as an empty phrase like "how are you?", then it is not appropriate. Why not? Obviously, in order to win an event or a match, one requires good luck. You have to play well, but you need your close decisions to work out well, and you need your opponents' decisions to work out poorly.
We all know that. It is theoretically impossible for everybody to have "good luck". So if you wish a particular pair "good luck", you are wishing other pairs "bad luck". I doubt that is what most well-wishers mean.
Similarly. I have trouble with "congratulations", and in particular when someone explicitly adds "I am happy you won". How about the pair that placed second? Are you "happy" they didn't win? I prefer to say "'well done, nice win" or words to that effect.
The only exception is when "good luck" or "congratulations" are offered by your opponents, then it is a gracious act of good sportsmanship.
Plus... it's free!