If you want to go into full whale mode, most of the megawhales I know have Apple devices specifically for the iTunes giftcard discounts. iTunes cards go on sale a lot more often than Google Play and the sales can be pretty steep, so you'll make back the money you spend on an iPad if you're a big enough whale. They buy in huge bursts during sales and hold onto the credit ahead of time, rather than buying on a whim as they go.

As for Google Play, the only sales I've seen are the Costco discounts where it's around 20% off or so, but those sales are pretty rare.