The biggest problem is the maps/adventures not easily accessible to the players.
Going back to the idea that this game will NOT dependent on the "luck" factor a treasure drop- map drops from adventure searches are the EXACT same thing as a treasure drop.
Maybe provide the adventures when the challenges are given (like holiday events, we're given the maps). or offer it as map fragments. You're already requiring resources from us. I do not see why providing us the map wouldn't be so bad. Or fix your quest designs so that the first quest - makes us pay X map fragments.
The game is currently unbalanced as is with the player gaps. The time required between the player levels is just staggering.