Incentive to upgrades collectors
Some people do not upgrade their mines and pumps because they just raid for recourses.
This creates a problem for other people who have no reason to raid them back (because they have hardly anything to steal) and overall it creates a shortage of resources in the game.
I believe that buildings should have more prerequisites than just the town hall level.
For example: Instead of a crossbow just requiring a TH9, now building a crossbow requires a TH9 and two level 11 elixir pumps.
Another example:
Instead of an inferno tower requiring only a TH10, now the inferno requires a TH10 and one level 6 dark elixir drill.
and so on for other buildings.