I kinda agree with the Upgrade System needing a slight revamp. Getting a Fail shouldn't penalize you since you do lose a stone (plus white if use) in the process. That's the only change I can think of really.
Regular dogi balls should be obtainable ingame as well as in Cash Shop for those who are unlucky while Rare should be earned by completing difficult tasks like a UD or something. Legendary dogi balls should be kept as event exclusive.
Brown Boxes should follow suit: available ingame as well as CS. Silver boxes should be a possible reward for killing the massive Ultras roaming Papaya as well as completing BID2 through BID4.
Drop system needs revamping so stones are easier to get, but white stones should be the rarest out of the bunch.