New Achievement to motivate people to max mines and collectors
There is little motivation for players to max their mines and collectors. In fact many people won't do it cause it will give attackers less loot if they don't have much outside of storages.
Motivate players to max these vital entry points for resources. Make it top out at TH7 with level 11 collectors/mines.
That can be the carrot now for the stick. Introduce an additional loot penalty for anyone who is th8 and doesn't have maxed collectors/mines. Make it an additional 5% penalty that stacks with the existing penalties.