I will start with spark prices:
They are just extremely overpriced, like really really overpriced. I suggest you lovering them to a reasonable point because this is just laughable. You know in my country people just don't use dollar bills to wipe themselfs. To give you a few examples:
For 10$ I can buy a new game, for 20$ I can buy even better game or 2 good ones, for 50$ I can buy amazing game that came out recently or 2.5 pretty good ones or 5 good ones, for 100$ I can probaly buy a game from the future so everyone would be jealous or just buy 2 awesome games that came out yesterday or buy 5 games or 10... you get the idea. That is all without considering sales that give you amazing opportunities. <- gamers logic.
I have some cookies and I am only going to sell each for 10$, I can also offer you 2 cookies for 20$, 5 cookies for 50$ and of course if you want the whole pack of cookies that is 10 of them you have to pay 100$. <- Your store logic.
Wanna buy some cookies or you might want to buy this awesome box of chocolate bars that everyone loves that is also happens to be on sale for only 7.50$?
Here is pretty good review of another free to play moba game from totalbiscuit that I am sure is going to help you rethink a few things:
He is talking about store prices as well.
cosmetics that if counting by spark price logic cost about 70$... really? Really?! Straight to the point, not reasonable.
From about 2 to 12 dollars for a portrait. Not reasonable. Also considering you get much better looking ones from completing achievements they just not worth it. I mean just look at those, monkey, creepy alien, some old ginger guy... and now look at this
they are actually pretty neat looking.
Please either make prices reasonable or redesign the whole store system making it reasonable.