I appreciate the effort. I would like to use them. My biggest problem is with how little they differentiate from one another. Particularly the spikes at the bottom seem useless, as most are placed behind the building.
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My suggestion would be:
Scout Tower: Completely remove the spikes at the ground and the top. Maybe remove the ladder.
Watch Tower: Recolor the roof to look like wood. Remove a couple of spike.
Cannon Tower: Recolor the roof and ladder, and possibly the entire scaffolding, to look like steel.