I was thinking that, since we are likely to never see the Spritely Prize Box again, or any of the boxes that contain the Hallow and Frosty Dragon Wings, Cat Tails, etc, why not just incorporate them into the prize pool for the Hallow and Frosty Prize Boxes? It makes more sense to put them there anyways, and I think people would like to see some new potential prizes like that in these classic boxes.
As for those would complain that this would introduce too many of these otherwise valuable accessories into the economy, 2 things: 1) there is a simple solution: Just make them a rare prize. For the Hallow Prize Box, make the Hallow Dragon Wings and Hallow Kat Tail like 2x as rare as the Haunted Aura, same thing applies to the Frosty Prize Box. Not too rare that it would require 100s of boxes to obtain, but rare enough that it is really rewarding to unbox them; 2) of course they will devalue, but using the above method will help to mitigate that devaluation a bit.
Also, as a side note, why don't you incorporate a Hallow version of the Frosty Warden Set? It would be something that would be cool to have around.
From my simple understanding, these additions to the prize boxes would be something that would be fairly easy to implement, and would really bring out some variety and real excitement in opening these prize boxes.
-Almond