Suggestion: Base Net Worth
This is a relatively simple idea, but I think it would be interesting to have a statistic as to the current net worth of your base. Your net worth would essentially be the combined value of all permanent investments in your base; i.e. building/wall upgrades, research upgrades, hero upgrades, etc. It would not account for temporary things such as resources stored in your storage units, value of troops, etc.
The net worth would be listed as 3 separate values; the gold, elixir, and dark elixir invested into your base. For a single number, the net worth could basically state what the gem equivalent is; i.e. how many gems would you have to spend to get all three of those resources (though it would neglect things like build time).
Anyway, I think it would be an interesting method of showing how much your base has grown.