I would like to see another type of weapon added - a drone unit. something that has a base it needs to return to weaponize and refuel, but that can be assigned to follow an enemy item till that enemy is killed or the drone is reassigned. 4 missles per flight, click on the base to activate and assign, it runs unmanned looking for "most advanced" threat when not assigned. maybe it could circle it's targets a couple squares out and lob missles in. gets upgraded by clicking on the base as well.
it would also be nice if you could move a defense position after it's been placed.
it would also be nice if the large $1000 cannons tracked a little ahead - they shoot based on current position, but then the enemy is gone by the time the slow moving shell reaches that spot. maybe just 1 block ahead would be better based on enemy current direction. in the real world, slower ammunition is compensated with predictive targeting.
it would also be nice if there were a "tactic" button - one that globally dictates how enemies are selected. toggle on for "most advanced threat" and toggle off for "closest threat to me" mode. In the real world, you might change tactics based on the ememies progress.