The ones I'm sad to have missed are:
-Nightmare
-Skeletal Dragon
-Money Badger
-Treasure Toucan
-Ornate Ocelot (would have to be made breedable then)
-Goldscale (would have to be made breedable then)
I would like to see those breedable (even if for a limited time) again. Other than the above short list there's nothing that comes to mind. I think all the other ones I've missed are "expendable" to me.
As for the Treasure animals: my stance still stands: until/unless they become breedable, or get significantly better gem-giving rates, or have good sale prices (like 200 gems), I shall stand down on them.