If you take away the negatives, it's just an opportunity cost like TMIT was saying. Part of what was interesting was those negatives, sure going all out on econ could make you crazy amounts of money but you risk an environmental meltdown if you push to hard (again for those that haven't played AC, +2 ECON meant +1 money on EVERY TILE throughout your empire. Bad environmental penalties meant randomly spawning hostile units). So the bonuses could be huge, but the penalties could be equally bad. I'm not suggesting that Civ should just mimic what AC did, I'm simply making the case that negative modifiers (carefully used) are not a penalty to fun. Far from it, when done right they can really make those "interesting choices" that Sid Meier talks about interesting.