Depends. Going heavy marketing is good only if you don't have the option to expand. If the used market is tight then throwing your extra money into marketing makes sense. Once you've reached a high CI you can come back and flood the routes your competition is flying without fear of losing alot of money. (Because high CI can negate high RI at the start of a route. High CI + route frequency = you control the route.)
The actual base strategy of this is to keep spending your cash on something. Be it aircraft expansion, marketing or something else. Never let your money just sit, because its a waste. Only times you should let your cash pile up is when you have nothing better to do/end game mode.
That said, Sami did tweak marketing not too long ago. It is a bit harder to reach higher CI levels now. So make sure your not over doing yourself to get at a high level. Though CI 60 sounds reasonable. Don't think you can get to CI 100 off less then 5 aircraft