How about this to improve Kill Streaks: Why not let us customise them? You could decide on your own pay load for helicopters etc.. That or Kill Streaks improve the more you use them, similar to how you unlock features for the guns. E.G. After 50 kills with a Pavelow it gains two additional flares. Or you could choose to increase it's offensive powers, higher fire rate for example. Customising Kill Streaks would give more depth to the game.
There are people who feel they are a little limited; this and the fact they get shot down too easily. This would allow for greater variety plus reward those who persever with certain streaks.