I don't know if this has been proposed before, but as an avid traveler in Torn, I'd like to see more benefits to entice people to choose the "life in the sky."
My suggestion is to add a frequent flyer system , for example, bigger luggage capacity (like in real life!) or faster travel time for destinations visited a certain number of times.
I'd suggest making this a challenge-based system, e.g. 1,000x, 2,000x, and so on, with different rewards for each milestone.
Cheers!