Too often do I encounter players who feel there is no need to waste Drachmas on walls and towers. Their cities look defenseless, but aren't, only showcasing how unnecessary they can be. 

Players who do this should be dramatically penalized (Walls and Towers should be much more powerful to the point that you MUST build them or be raided by a few swords or easily lose all your traps, etc...something!), forcing players to build their cities like a "real" city, not trying to cheat the system.