Suggestion: Automatic storage fill from full mines and collectors
As things get really expensive in high townhall levels, why not have an automatic storage fill when mines and collectors reach full capacity. Once a mine or collector reaches full capacity is automatically moves into the main storage buildings. The setting like the wall upgrades can begin at a given lvl, like at collector or mine level 9.
obviously raiding is a large part of the game, so rewarding a chief for having a base that no one wants to 'cheap raid', like with goblins only, could be a nice upgrade.