Okay I have 30 of every coin now and I feel I should comment.
People in the comments does not seem to have understood the game
1. more copper cois are good as the shockwave achievment+the 30 copper upgrades makes them better than silver until you get 30 silver and you don't want to transform them into silver
2. Its not a game of odds. when you have a good amount of coins you have an expected value and a pretty fixed money per second
As for my oppinion, I think 30 coins for upgrades in a non incremental game is very hard to get and boring. I sugest implementing prestige, platinum coins and more upgrade for helpers as others have already said and I would go for cosmetics and temporary buffs for monetization