I have completed constructing all available buildings but I have noticed there are still areas that may be opened for 500 drachmas. What I am wondering is that if I do pay to open them can I then use that freed space for additional decor (to raise my City Defense Bonus)? From the look of the space I would guess I could fit 4 '+9' units in each of the four large squares I would be granted.

Also, I am curious as to what all you defense experts out there think about is the cost worth the gain. On 1 hand it seems too pricey to pay 500 drachmas simply for access to the space. If my judgement is correct the most a player could gain would be a bump of +144 (4 squares, each able to fit 4 units, each of those having a +9 defense increase.

I still think this is 1 of the loussiest parts of the game due to how expensive it is to build powerful towers, gates, and assorted statues, weapons, and traps inside the city walls. there is simply no way to obtain these things without purchasing NUMEROUS drachma packages.