As others have said, I think the biggest issue is just the money collection. I think you could go one of two routes:
-If money were automatically collected and then prices were tuned to reflect the increased money you'd be getting then it'd be more fun to focus on hitting the ball and killing zombies.
-Alternatively you could just make money NOT despawn. The main issue is that money despawns so quickly that by the time the horde of zombies have walked far enough away from the money for me to circle around and pick it up it's already flashing and despawning.