My view is that the word should be common but I also think that if a word is on the cusp, so to speak, it's probably safer to leave it as rare. Most people's overall objective in playing the game is to get a rosette and every word changed from rare to common means one more word to find, in any puzzle in which the word can be played, in order to achieve that goal.
As always, Alan, you can't please all the people all the time.