Mines are probably the best investment in EB, a mine producing 600 per turn will pay for itself in 24turns/ 4years after that it's pure profit, and in a game where you can play over 1000 turns. I wish my investments had a return like that!
Some provinces, such as Pella, with a character with the right traits can earn several thousand a turn.
I guess the 2000 per turn is a throwback to the two moves in RTW, plus the EB turn wanted to simulate different resources being worth more.