Give rewards for beating certain people in PvP/Base.
For those who maintain their win streak, give them an incentive, everyone loves to beat the **** outta erreryone, let em get rewarded for it. Erreryone likes the underdog who miraculously beats the pro, give em a reward for his efforts.
Have an achievement system, beat certain mobs certain amount of times with certain amount of health and earn a prize.
ex. Kill 100 nimba's as a ram with ion wave without taking any damage on sector level so and so.