For the demon guys, don't bother using the wizard hero. You pay more to heal your front line guys, and heroes cost less to repair. Therefore, if you have two of the soldiers, they will take a huge chunk out of your iron, but with a hero, the cost will be much less.
I'm running into a bug with the garbage collector script. I hold down shift, but can still only use it once and then it's on CD forever. Great game otherwise.