pixel_player50658624
It depends on your situation in the game also.
In the beginning, you can get a lot out of playing shop stories for 100 gems. Great equipment, much better that in the main shop.
Check it out here
https://forum.pixelfederation.com/diggysadventure/d/187533-camp-equipment-spreadsheets-for-older-stories-available-in-shop
Personally I started upgrading energy saver and experience booster only when I had really enough gems, and I did it from time to time, when I had enough of them.
But then, I don’t buy gems. For those who do, it’s a different story.