I think it comes down to in what scale you play your campaign. I may work very good in a campaign of 6-10 players while in my small campaign, with only three, the cost of giving away better income becomes huge in proportion to what you get. Compare the 10 player campaign, where one of your opponents only gain anything from your upgrade in 1/9 of her played games, to the smallest possible campaign (2 players) where your upgrade gives your opponent more income in 100% of her games (and every game after that you have to face an opponent who got that advantage, while giving away even more to later encounters...).