If you don’t need Hobbit Building Crew items, you can just buy Monday Mystery chests.
These chests cost 5 mithril, each. They appear only on Mondays, in the game’s shop.
The Monday Mystery chests can contain troops, other type of chests, speed potions etc. Even 50 or 100 other Monday Mystery chests.
I remember growing from 600.000 to 1.000.000 might just because I was lucky enough to get 100 Monday Mystery chests from one chest. And then I got 50 extra Monday Mystery chests also from one of those 100 chests.
Don’t bother to buy speed potions or resources.
Also, you can buy Galandriel’s tokens. But those are more expensive than the Monday Mystery chests and the price/quantity/reward, is worse than what you get from Monday Mystery chests.