Upgrade with Xplodium?

Is it possible to allow us to upgrade our guns with earned Xplodium? Also if not, allow us to earn War Bucks in endless and campaign modes! I have bought some War Bucks for 5 bucks and it didn't seem to get me anywhere. Also the Guns that require War Bucks to purchase are EXTREMLY expensive. I don't have 50-200 dollars to spend on a gun that I might not even like!:( also I have completed the game in campaign mode with all gold stars except the very last mission,(Silver star) do you have more missions coming? Seems a lot more basic than the first one. Thanks:)