Currently when you click on a tile the stats displays show the impact of that tile. So if you click on something like the town you can see it is producing 1 currency per turn, while consuming 10 power per turn.
I may or may not implement your solution. Because problems begin to arise when you select a pre existing tile. Your method would not be clear if the number on the left (12 in your example with the trees) is the actual sum of all the tiles affecting that stat, or all the tiles but the one selected. You'd also still have the problem of the stats for one tile instead of global stats being there for the majority of the game. I think it would be a better solution than the current implementation but definitely still needs some work.
I think I'll do a quick fix. I can add some text that says what the stats display is showing (E.g. global, coal plant, plains), and deselect tiles on a new turn. Not perfect but definitely an improvement.
I'll try my best to improve that aspect of the UI. Thanks for your feedback, I'll try to give the game an update in a week or two.