If I have spent time or food on leveling up, ranking up, or empowering a dragon it would be nice to be compensated back for it when selling it. For instance we just had the event asking to breed nature and electric dragons which I then used the resulting nature dragons to empower one nature dragon to 5 stars. During these events and we get a lot of basic element dragons like fire, Terra, nature etc it would make sense to utilize the babies for further empowering but these basic element dragons don't gain much advantage in battles even when 5 starred. Getting additional coin when selling empowered dragons seems logical. Also, getting more coin for leveled up dragons would help compensate the food cost.