I personally find wooden walls to be practically useless. Other than delaying an assault by about a turn or two, they give very little advantage to the defenders. I have to arc my missiles over the wall because apparently my men are all fat lards and they would cause the whole thing to collapse or something.

The ONLY wall type worth having is a STONE wall. The only problem with that is that my frontier towns are the ones getting attacked. They arent large or advanced enough to build stone walls most of the time. While those that are able to construct them, tend to be in the heart of my empire, far away from enemy lines, and are normally my troop producing/economic powerhouses and are therefore most likely far too busy building more and better militray/economic improvements and dont have the time (or even a good reason) to construct a stone wall. If anything the wall should be upgradeable to at least a STONE wall once you hit large town status or something, either that or make it so you can put troops on the second tier wooden wall. It may not be that great of a height advantage, but its something...ok nevermind...just give me stone walls...please?