Okay the store is useless without shiny. Now what I think would be a good idea is making another type of in-game currency, that is easier to get and you can buy ''cheap'' items.
So what I mean is like make premium items cost shiny, and normal items just cost some other currency in the store. And leave everything else like buildings with resources. + if you think this would probably be a lot better.
There should be something where it tells you what each training raises more specifically.. Like defense raises health, power raises attack, etc. I know it's kinda logical but still. 3.3/5