Just wanted to add that people who just want to go through content will/should be pleased enough with their reward. Those who wants a challenge but still be rewarded for their effort will be able to do so in those capped runs while not giving them such an advantage over others that it makes capped runs mandatory.

Of course, right now the level 50 dungeon is capped to level 50 so either make the special rewards available now OR later after the level cap is raised so it gives those dungeons (assuming there will be more coming) a replay value.