What is the point of armor? It is a defensive measure, it is to you protect you from getting injured or killed during battle. The question is, do spikes enhance the defensive qualities of the armor. I don't think they do, and it would add difficulty in the manufacturing process. If I am a rabbit wearing armor, fighting a wolf, and said wolf bites down on my shoulder will the spikes improve the defense or kill the wolf, the answer in both is no. The armor defeats the teeth of the wolf (its job), if it has spikes it might make the wolf hurt more, but it really does not add much. Further, iron was used to create armor, and iron dulls and rusts rather easily, so even if the fabrication wasn’t that much more difficult, the maintenance would be for sure. Only now the surface area is exponentially greater, so even MORE places for rust to occur. Rusty armour means less effective armour, so you’re liable for a tradeoff. A final thought, spiked armour would be rather ineffective unless the opponent was unarmoured, so at best, sporting spikes don’t even really add much to your options. You also want enemy's weapons to have a direction to glance off of you when hit, this is less likely if your body’s surface is made up of spikes that could “catch” weapon strikes that might actually go into places like your neck. Why would you help your enemy by giving him more hand holds to grapple you with & more guides for his weapons to find you body? I really don't see the point of adding spikes, if you want to hit a wolf in the face with something pointy, a sword or polearm would be much better and far more effective anyhow.