I personally upgrade defense to get the 4 basic upgrades completed. I agree that normally giving a no dachi better charge should be a good idea, but it really isn't. I had to delete all mine when I noticed. Anything above 20-25 charge doesn't really matter as you won't hit more people because of it. In this case the "make the unit even better at what it's meant for" policy doesn't work. I have to say that I would prefer it if it did.