So to add more life to the city I have some ideas to add some player interactivity.
TURF WARS:
Within a given zone in a city, not the city itself, there are 3-4 enemy groups. As players fight and defeat enemies of one group, lets say hellions, the other enemy groups, example trolls and outcasts, become stronger. Their level does not increase, would make it too tough on lower level players, but more Lt and bosses appear as well a noticeable but not complete increase in their spawn groups. If one enemy group gains a large enough control, by players attacking all other enemy types, then that group starts to spawn a rare (generic) named enemy (maybe elite boss) also that mobs grafitti starts to appear around the city. As the enemy group in power is taken down by players or after a reset time the numbers/control returns to normal. Extra incentive for players is to give a badge for killing the named spawn when a certain group gains total control. Let me clarify: when an enemy group gains complete control all other enemy groups still spawn.
CITY RECOGNITION:
Within a city zone, not the entire city itself, players can gain recognition from the citizens of the city. As they do mission within that area, take to the streets fighting mobs, slay a giant monster or two, maybe even fight a fire, they gain recognition within the zone. If this number becomes high enough then citizens around the city start to mention the players name to a noticeable amount (more than the current). If it goes up even more then that then a poster or two of the hero appears in the city. Wanted poster for villains and a poster of praise for heroes. If the hero reaches a high enough status of recognition they become hero/villain of the day. Their face appears on billboards; blimps, citizens praise/curse them, and maybe a badge if they become head hero/villain for all of the cities zones (not at once), and possibly a small amount of merits obtainable only once for each city.
Enemy Malice:
As players fight and take down enemies of a certain group that group gains malice towards the player. At a certain level of malice enemies curse the players name in anger then in fear. At a higher level grafitti appears of the hero/villan saying naughty but pg things. At the highest level a hit is placed upon them in which an ambush attempted upon them (after exiting a mish or something). After the ambush or after some time has passed the malice subsides.