You might have the most robust game I've played, and this is right up my alley so my mind is going a mile a minute with thoughts. But since I really don't want to bombard you, I'll offer one thing: I think the redirect-tubes you have would make more sense as a way to corral the mobs, as opposed to projectiles. If they're made the cheapest, you have a good way to balance resource management, and force people to carefully strategize layouts.