Tycoon World is fabulously complex, but it is lacking in key element of game theory. What do Rock-Paper-Scissors, Starcraft, and Civilization IV all have in common? Each game has distinct strategies that will lead to victory and each strategy has a weakness. Rock beats scissors, but is bested by paper. Zerglings beat Dragoons, Zealots beat Zerglings. In Civ you can win by military might, by colonizing Alpha Centauri, or culturally. But in Tycoon World there is only one path to victory - make cars, maintain a steady stream of ROI avoiding days of low or negative ROI. It's the lack of diverse methods of attaining victory that is the games biggest weakness.
Not only is victory restricted to those who make cars, it's also restricted to those who sell little of what they make to other players. You can't win by making loads of steel and selling it because you won't get enough vendor score or manufacturing score. You can't win by making loads of cars and selling them to other players because you won't get a high enough vendor score. This narrow path to victory reduces player interaction and squelches alliances and cooperation.
The questions are how to introduce new paths to victory and how to reward cooperation. One thing is for sure, any changes that are made to the game need to be balanced and well thought out. Any path to victory should be able to provide a clear advantage if few people chose it, and a clear disadvantage if many people chose it.
(I sure hope you have the game "rock, paper, scissors" in Germany or my analogy will be lost). In Tycoon World we only have rock.
http://en.wikipedia.org/wiki/Rock-paper-scissors