My company image is pegged at 22% in one of my games, but my LF's are consistently around 80% with fares set to default.
At this point, why should I invest money into making my CI higher? Seems like a waste of money to me.
CI does two things;
1) If you compete with other airlines, passengers prefer the airline with the higher/highest CI
2) Higher CI gets you more First/Business Class Passengers in bigger aircraft (maybe not important if you fly Dash8 with Business/First Class)
And given what Curse has said, there may not be any reason to increase your CI.
In some games I keep a CI of 60. In other games I go for 90. And in others I go all the way to 100.
It just depends on the situation I'm going to find myself in.