As others mentioned, GPDs would be a great sale. I'd also love for a sale on the dragon stable/upgrades for it, egg nests, and the breeding roost.

I'd also love to see a steeper sale on gold. I know the 30% off randomly rolls around, but it'd be nice to have an even better sale for the inevitable holiday dragons coming around. Especially for us newer caretakers who don't have GPDs to save up gold, and will have a massive selection of dragons that we're seeing for the first time.