It sounds very cool and I would like to play it, but I casted a vote of "Yes, but with improvement" because I think that there can be a cool twist in the game. This can be anything, like maybe attackers can activate bonuses to give them all extra damage, become faster, or even invincibility for a certain time. And maybe defenders can build walls so that attackers will be slowed down. However, I just think the game idea is too simple: Attack and Defend. I will probably reply to this post again if I have an idea that might improve the game to make it more fun.
For the red spot, I think it should be a small store. Because who would want a hospital beside a gas station?