I do like the second and third option. This would make a lot of difference in the tactical aspect of the game.
With the first option I disagree, yes for a smaller player this is understandable but for a big player the'se upgrades need to be higher cost since otherwise it will be too easy to infinite max the upgrades. For now the're is like a capacity limitation and for bigger players they need to choose between upgrading buildings or upgrade units.
Some choose combat over growth and other players think longterm and prefer higher buildings and better sustainable economy.
So with the first point, I understand if you are a smaller player to keep up with the big boys. But for big boys, its kinda necessary to keep the game balanced and interesting.