Thank you for the comment!
I agree, there are plenty of (even low hanging) fruits to pick up, but I did not have enough time (and at the end energy) to implement them. The original idea was for the enemies to sacrifice and destroy/disable some turrets. Maybe they could even calculate which tower would be best for them to destroy.
The game obviously needs something to make the gameplay longer, either more levels, or some sort of puzzle mechanics - f.e. what is the least budget to survive X amount of enemies. And wanted it to be impossible to beat with the starting budget, so you would need to die and get more money, but apparently 100 is enough.