I'm not sure I'd call a bike computer a luxury item: for those who either train or navigate, or both, they are pretty much essential. Ok, maybe getting a Garmin 1030, instead of the 830, might be a little luxurious, but for some the larger screen is an essential.

Id suggest mechanical Ultegra or Dura Ace over 105 is a luxury. Of course, Di2 means you have to go Ultegra as a minimum.

Id also agree with carbon bars and stem being luxury items.