normally, CI should stay above 0 even without marketing as long as your company is doing good. Reasons for negative CI are for example delays/cancellations, poor maintenance, or unhappy staff.
The only way to raise CI is general marketing. How much it increases is linearly correlated to the amount of money you spend on marketing. The costs however rise with every new destination.
Spending $47k on marketing sounds very small, but it could be ok if you only have 2-4 destinations.