I just created another base 322 nm from my first base. Both airports have a gate rental price of 250k, and I had a DOC of about 5 million. When I created the base, my airline value increased dramatically (Almost tipped 1 billion), and my DOC increased by about three million in a matter of hours (I had two planes ready for use at that airport before I created it). My expenses also became "smaller" because I created routes from the new base to the destinations I allready had, which makes the gates at the destinations "cheaper" because you make more profit of that destination, if you understand
BTW, competition is more likely to be harder the higher gate rental price there is