First, maybe add a respec for captains and vehicles, maybe for like 100 cash or a few videos. Late game when you have grinded all reliable resources and actually unlocked a useful vehicle/captain you spend days just waiting to get the few materials to upgrade once.
Secondly, every time a you release a new vehicle or captain. Make the other ones obtainable “free” or do a tier set up, I.e. every time a new vehicle is released, the last one that was 5.99* is now accessible through cash/videos/achievements. Then the one that was 9.99 drops to 5 and so forth.
Lastly, take a look at chance percentages on crates. I feel, at least for me, it is a little bugged, on silver key crates I earn about 50/ 50 between common and uncommon. On gold key crates I’ve earned more purple, which is only 2 times, than I have blue. It almost certain, I’m getting green with a small percent of getting purple rarely blue.